Enhance FIPS, DualStack, IMDS Endpoint Support

[YakDriver]

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Closes #20824
Requires hashicorp/aws-sdk-go-base#88
Relates aws/aws-sdk-go#3938

Running a similar config to #20824:

provider "aws" {
  region = "us-west-2"

  assume_role {
    role_arn = "arn:aws:iam::012345678901:role/Litnupras"
  }

  endpoints {
    sts = "https://sts-fips.us-west-2.amazonaws.com"
  }
}

data "aws_caller_identity" "this" {}

The current provider throws the error shown in #20824. However, with a provider built from this branch, this is the result (the correct result since it creates no resources):

% terraform apply

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration and found no differences, so no changes are needed.

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Output from acceptance testing (randomly chosen to make sure things work as normal):

% make testacc TESTS=TestAccS3Object_ PKG=s3     
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/s3/... -v -count 1 -parallel 20 -run='TestAccS3Object_'  -timeout 180m
--- SKIP: TestAccS3Object_nonVersioned (1.43s)
--- PASS: TestAccS3Object_noNameNoKey (4.72s)
--- PASS: TestAccS3Object_withContentCharacteristics (37.20s)
--- PASS: TestAccS3Object_objectBucketKeyEnabled (42.14s)
--- PASS: TestAccS3Object_defaultBucketSSE (44.44s)
--- PASS: TestAccS3Object_etagEncryption (43.17s)
--- PASS: TestAccS3Object_bucketBucketKeyEnabled (44.73s)
--- PASS: TestAccS3Object_sse (44.75s)
--- PASS: TestAccS3Object_kms (45.31s)
--- PASS: TestAccS3Object_updates (71.94s)
--- PASS: TestAccS3Object_updateSameFile (72.64s)
--- PASS: TestAccS3Object_contentBase64 (30.58s)
--- PASS: TestAccS3Object_ignoreTags (74.07s)
--- PASS: TestAccS3Object_updatesWithVersioningViaAccessPoint (74.38s)
--- PASS: TestAccS3Object_updatesWithVersioning (76.49s)
--- PASS: TestAccS3Object_content (33.55s)
--- PASS: TestAccS3Object_source (33.57s)
--- PASS: TestAccS3Object_metadata (100.18s)
--- PASS: TestAccS3Object_objectLockLegalHoldStartWithNone (102.18s)
--- PASS: TestAccS3Object_sourceHashTrigger (60.50s)
--- PASS: TestAccS3Object_empty (30.88s)
--- PASS: TestAccS3Object_acl (103.58s)
--- PASS: TestAccS3Object_objectLockLegalHoldStartWithOn (61.97s)
--- PASS: TestAccS3Object_tagsLeadingMultipleSlashes (125.72s)
--- PASS: TestAccS3Object_tagsMultipleSlashes (125.82s)
--- PASS: TestAccS3Object_tagsLeadingSingleSlash (128.17s)
--- PASS: TestAccS3Object_tags (128.34s)
--- PASS: TestAccS3Object_objectLockRetentionStartWithNone (87.50s)
--- PASS: TestAccS3Object_storageClass (150.26s)
--- PASS: TestAccS3Object_objectLockRetentionStartWithSet (110.37s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/s3	156.292s

[ewbankkit]

Also need to update website/docs/index.html.markdown.

[ewbankkit]

LGTM 🚀.

% make testacc TESTARGS='-run=TestAccEC2Instance_basic' PKG=ec2
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/ec2/... -v -count 1 -parallel 20  -run=TestAccEC2Instance_basic -timeout 180m
=== RUN   TestAccEC2Instance_basic
=== PAUSE TestAccEC2Instance_basic
=== CONT  TestAccEC2Instance_basic
--- PASS: TestAccEC2Instance_basic (117.74s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/ec2	121.414s
% AWS_USE_FIPS_ENDPOINT=true make testacc TESTARGS='-run=TestAccEC2Instance_basic' PKG=ec2
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/ec2/... -v -count 1 -parallel 20  -run=TestAccEC2Instance_basic -timeout 180m
=== RUN   TestAccEC2Instance_basic
=== PAUSE TestAccEC2Instance_basic
=== CONT  TestAccEC2Instance_basic
--- PASS: TestAccEC2Instance_basic (130.23s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/ec2	133.764s

[github-actions]

This functionality has been released in v4.0.0 of the Terraform AWS 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]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.