Add resource document to google_firestore

[ScottSuarez]

Added resource document to google_firestore
Closes 3950

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

`google_firestore_document`

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 6 files changed, 828 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 6 files changed, 828 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 65 insertions(+))
TF OiCS: Diff ( 8 files changed, 218 insertions(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=160960"

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 6 files changed, 828 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 6 files changed, 828 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 65 insertions(+))
TF OiCS: Diff ( 8 files changed, 218 insertions(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=160960"

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 7 files changed, 855 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 7 files changed, 855 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 65 insertions(+))
TF OiCS: Diff ( 8 files changed, 218 insertions(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=161098"

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 7 files changed, 880 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 7 files changed, 880 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 65 insertions(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=161099"

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 7 files changed, 879 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 7 files changed, 879 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 65 insertions(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=161195"

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 7 files changed, 880 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 7 files changed, 880 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 65 insertions(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=161291"

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 7 files changed, 880 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 7 files changed, 880 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 65 insertions(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=161295"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccDataSourceComposerEnvironment_basic|TestAccDataSourceComputeResourcePolicy|TestAccDataSourceSpannerInstance_basic|TestAccActiveDirectoryDomainTrust_activeDirectoryDomainTrustBasicExample|TestAccBigqueryDataTransferConfig|TestAccCloudSchedulerJob_schedulerJobHttpExample|TestAccComposerEnvironment_withUpdateOnCreate|TestAccComputeGlobalForwardingRule_globalForwardingRuleHttpExample|TestAccComputeGlobalForwardingRule_globalForwardingRuleInternalExample|TestAccComputeManagedSslCertificate_managedSslCertificateBasicExample|TestAccComputeTargetGrpcProxy_targetGrpcProxyBasicExample|TestAccComputeTargetGrpcProxy_update|TestAccComputeTargetHttpProxy_targetHttpProxyBasicExample|TestAccComputeTargetHttpsProxy_targetHttpsProxyBasicExample|TestAccComputeUrlMap_urlMapBasicExample|TestAccComputeUrlMap_urlMapTrafficDirectorRouteExample|TestAccComputeUrlMap_urlMapTrafficDirectorRoutePartialExample|TestAccComputeUrlMap_urlMapTrafficDirectorPathExample|TestAccComputeUrlMap_urlMapTrafficDirectorPathPartialExample|TestAccComputeUrlMap_urlMapHeaderBasedRoutingExample|TestAccComputeUrlMap_urlMapParameterBasedRoutingExample|TestAccComputeUrlMap_defaultRouteActionTrafficDirectorUpdate|TestAccComputeUrlMap_defaultRouteActionTrafficDirectorPathUpdate|TestAccComputeUrlMap_trafficDirectorPathUpdate|TestAccFirestoreDocument_firestoreDocumentBasicExample|TestAccFirestoreDocument_firestoreDocumentNestedDocumentExample|TestAccFirestoreDocument_update|TestAccFilestoreInstance_filestoreInstanceBasicExample|TestAccFilestoreInstance_update|TestAccOSLoginSSHPublicKey_osLoginSshKeyExpiry You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=161305"

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 7 files changed, 880 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 7 files changed, 880 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 65 insertions(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=161309"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccDataSourceComposerEnvironment_basic|TestAccDataSourceComputeResourcePolicy|TestAccDataSourceSpannerInstance_basic|TestAccActiveDirectoryDomainTrust_activeDirectoryDomainTrustBasicExample|TestAccBigqueryDataTransferConfig|TestAccCloudSchedulerJob_schedulerJobHttpExample|TestAccComposerEnvironment_withUpdateOnCreate|TestAccComputeGlobalForwardingRule_globalForwardingRuleHttpExample|TestAccComputeGlobalForwardingRule_globalForwardingRuleInternalExample|TestAccComputeManagedSslCertificate_managedSslCertificateBasicExample|TestAccComputeTargetGrpcProxy_targetGrpcProxyBasicExample|TestAccComputeTargetGrpcProxy_update|TestAccComputeTargetHttpProxy_targetHttpProxyBasicExample|TestAccComputeTargetHttpsProxy_targetHttpsProxyBasicExample|TestAccComputeUrlMap_urlMapBasicExample|TestAccComputeUrlMap_urlMapTrafficDirectorRouteExample|TestAccComputeUrlMap_urlMapTrafficDirectorRoutePartialExample|TestAccComputeUrlMap_urlMapTrafficDirectorPathExample|TestAccComputeUrlMap_urlMapTrafficDirectorPathPartialExample|TestAccComputeUrlMap_urlMapParameterBasedRoutingExample|TestAccComputeUrlMap_urlMapHeaderBasedRoutingExample|TestAccComputeUrlMap_trafficDirectorPathUpdate|TestAccComputeUrlMap_defaultRouteActionTrafficDirectorUpdate|TestAccComputeUrlMap_defaultRouteActionTrafficDirectorPathUpdate|TestAccFirestoreDocument_firestoreDocumentBasicExample|TestAccFirestoreDocument_firestoreDocumentNestedDocumentExample|TestAccFirestoreDocument_update|TestAccFilestoreInstance_filestoreInstanceBasicExample|TestAccFilestoreInstance_update|TestAccOSLoginSSHPublicKey_osLoginSshKeyExpiry You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=161315"