New Data Source: azurerm_policy_assignment

[magodo]

This PR implements a new data source azurerm_policy_assignment.

NOTE: Currently, this PR is depending on a local version of github.com/hashicorp/go-azure-helpers package. Until, hashicorp/go-azure-helpers#112 is merged, we can change to using the upstream one and go on reviewing this PR.

Fixes #16491.

Test

> TF_ACC=1 go test -v -timeout=20h ./internal/services/policy -run='TestAccDataSourceAssignment_builtinPolicy|TestAccDataSourceAssignment_identity'
=== RUN   TestAccDataSourceAssignment_builtinPolicyBasic
=== PAUSE TestAccDataSourceAssignment_builtinPolicyBasic
=== RUN   TestAccDataSourceAssignment_builtinPolicyComplete
=== PAUSE TestAccDataSourceAssignment_builtinPolicyComplete
=== RUN   TestAccDataSourceAssignment_identity
=== PAUSE TestAccDataSourceAssignment_identity
=== CONT  TestAccDataSourceAssignment_builtinPolicyBasic
=== CONT  TestAccDataSourceAssignment_identity
=== CONT  TestAccDataSourceAssignment_builtinPolicyComplete
--- PASS: TestAccDataSourceAssignment_builtinPolicyBasic (248.56s)
--- PASS: TestAccDataSourceAssignment_builtinPolicyComplete (306.67s)
--- PASS: TestAccDataSourceAssignment_identity (438.85s)
PASS
ok      github.com/hashicorp/terraform-provider-azurerm/internal/services/policy        438.866s

[katbyte]

LGTM 🍁

[github-actions]

This functionality has been released in v3.11.0 of the Terraform Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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