Add aws_db_instances data source

[Mongey]

Description

This adds a datasource for aws_db_instances

References

Closes #17634.
Closes #21402.

Output from Acceptance Testing

$ make testacc TESTS=TestAccRDSInstancesDataSource_filter PKG=rds                                                                                                                     ==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/rds/... -v -count 1 -parallel 20 -run='TestAccRDSInstancesDataSource_filter'  -timeout 180m
=== RUN   TestAccRDSInstancesDataSource_filter
=== PAUSE TestAccRDSInstancesDataSource_filter
=== CONT  TestAccRDSInstancesDataSource_filter
--- PASS: TestAccRDSInstancesDataSource_filter (556.20s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/rds        562.672s
...

[github-actions]

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[ewbankkit]

LGTM 🚀.

% make testacc TESTARGS='-run=TestAccRDSInstancesDataSource_' PKG=rds ACCTEST_PARALLELISM=3
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/rds/... -v -count 1 -parallel 3  -run=TestAccRDSInstancesDataSource_ -timeout 180m
=== RUN   TestAccRDSInstancesDataSource_filter
=== PAUSE TestAccRDSInstancesDataSource_filter
=== CONT  TestAccRDSInstancesDataSource_filter
--- PASS: TestAccRDSInstancesDataSource_filter (553.48s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/rds	561.079s

[ewbankkit]

@Mongey Thanks for the contribution 🎉 👏.

[github-actions]

This functionality has been released in v4.47.0 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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