Add RDS Aurora Global Cluster Data Source

[theherk]

Description

Add a data source matching the resource reader for `aws_rds_global_cluster

Unfortunately, I created this before seeing that #37286 existed. However it is currently out of sync, so perhaps this is still warranted.

I did start with the latest framework type coming from skaff, but had some issues with tagging, and thought it would be better to keep consistent with the matching resource anyway, so the sdk type is used here.

Relations

• Part of Add data source for aws_rds_global_cluster #13289
• Closes New data source: aws_rds_global_cluster #20171

Output from Acceptance Testing

ᐅ make testacc TESTS=TestAccRDSGlobalClusterDataSource PKG=rds ACCTEST_PARALLELISM=4
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.23.5 test ./internal/service/rds/... -v -count 1 -parallel 4 -run='TestAccRDSGlobalClusterDataSource'  -timeout 360m -vet=off
2025/03/05 14:11:27 Initializing Terraform AWS Provider...
=== RUN   TestAccRDSGlobalClusterDataSource_basic
=== PAUSE TestAccRDSGlobalClusterDataSource_basic
=== RUN   TestAccRDSGlobalClusterDataSource_withTags
=== PAUSE TestAccRDSGlobalClusterDataSource_withTags
=== CONT  TestAccRDSGlobalClusterDataSource_basic
=== CONT  TestAccRDSGlobalClusterDataSource_withTags
--- PASS: TestAccRDSGlobalClusterDataSource_basic (16.86s)
--- PASS: TestAccRDSGlobalClusterDataSource_withTags (17.51s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/rds	22.904s

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