resource/aws_iam_policy: Do not iterate over all IAM Policies when ARN supplied

[gdavison]

No longer iterates over all IAM Policies in aws_iam_policy data source when ARN is supplied. Also fixes bug where tags are not retrieved.

Closes #25533.
Closes #25537.
Closes #19878.

Output from acceptance testing:

$ make testacc PKG=iam TESTS=TestAccIAMPolicyDataSource_

--- PASS: TestAccIAMPolicyDataSource_awsManagedArn (26.32s)
--- PASS: TestAccIAMPolicyDataSource_arnTags (29.29s)
--- PASS: TestAccIAMPolicyDataSource_arn (30.15s)
--- PASS: TestAccIAMPolicyDataSource_nameAndPathPrefixTags (30.17s)
--- PASS: TestAccIAMPolicyDataSource_nameAndPathPrefix (30.49s)
--- PASS: TestAccIAMPolicyDataSource_nameTags (39.02s)
--- PASS: TestAccIAMPolicyDataSource_name (40.39s)
--- PASS: TestAccIAMPolicyDataSource_nonExistent (126.49s)

[ewbankkit]

LGTM 🚀.

% make testacc TESTARGS='-run=TestAccIAMPolicyDataSource_' PKG=iam ACCTEST_PARALLELISM=3
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/iam/... -v -count 1 -parallel 3  -run=TestAccIAMPolicyDataSource_ -timeout 180m
=== RUN   TestAccIAMPolicyDataSource_arn
=== PAUSE TestAccIAMPolicyDataSource_arn
=== RUN   TestAccIAMPolicyDataSource_arnTags
=== PAUSE TestAccIAMPolicyDataSource_arnTags
=== RUN   TestAccIAMPolicyDataSource_name
=== PAUSE TestAccIAMPolicyDataSource_name
=== RUN   TestAccIAMPolicyDataSource_nameTags
=== PAUSE TestAccIAMPolicyDataSource_nameTags
=== RUN   TestAccIAMPolicyDataSource_nameAndPathPrefix
=== PAUSE TestAccIAMPolicyDataSource_nameAndPathPrefix
=== RUN   TestAccIAMPolicyDataSource_nameAndPathPrefixTags
=== PAUSE TestAccIAMPolicyDataSource_nameAndPathPrefixTags
=== RUN   TestAccIAMPolicyDataSource_nonExistent
=== PAUSE TestAccIAMPolicyDataSource_nonExistent
=== CONT  TestAccIAMPolicyDataSource_arn
=== CONT  TestAccIAMPolicyDataSource_nameAndPathPrefix
=== CONT  TestAccIAMPolicyDataSource_name
--- PASS: TestAccIAMPolicyDataSource_arn (16.40s)
=== CONT  TestAccIAMPolicyDataSource_nameTags
--- PASS: TestAccIAMPolicyDataSource_nameAndPathPrefix (16.45s)
=== CONT  TestAccIAMPolicyDataSource_arnTags
--- PASS: TestAccIAMPolicyDataSource_name (20.14s)
=== CONT  TestAccIAMPolicyDataSource_nonExistent
--- PASS: TestAccIAMPolicyDataSource_arnTags (12.70s)
=== CONT  TestAccIAMPolicyDataSource_nameAndPathPrefixTags
--- PASS: TestAccIAMPolicyDataSource_nameTags (16.21s)
--- PASS: TestAccIAMPolicyDataSource_nameAndPathPrefixTags (12.79s)
--- PASS: TestAccIAMPolicyDataSource_nonExistent (121.90s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/iam	145.937s

[ewbankkit]

Needs a CHANGELOG entry.

[gdavison]

Needs documentation, too :)

[ewbankkit]

Extra space.

Suggested change

	data-source/aws_iam_policy: Now loads tags.
	data-source/aws_iam_policy: Now loads tags.

[github-actions]

This functionality has been released in v4.20.0 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]

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