Add aws_identitystore_group_memberships data source

[liath]

Description

Adds a data source for listing the members of an Identity Store Group. Part of a few PRs to cover #26770.

Relations

Relates #26770

References

https://docs.aws.amazon.com/cli/latest/reference/identitystore/list-group-memberships.html
https://docs.aws.amazon.com/singlesignon/latest/IdentityStoreAPIReference/API_ListGroupMemberships.html

Output from Acceptance Testing

$ make testacc TESTS=TestAccIdentityStoreGroupMembershipsDataSource PKG=identitystore
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.22.2 test ./internal/service/identitystore/... -v -count 1 -parallel 20 -run='TestAccIdentityStoreGroupMembershipsDataSource'  -timeout 360m
=== RUN   TestAccIdentityStoreGroupMembershipsDataSource_basic
=== PAUSE TestAccIdentityStoreGroupMembershipsDataSource_basic
=== CONT  TestAccIdentityStoreGroupMembershipsDataSource_basic
--- PASS: TestAccIdentityStoreGroupMembershipsDataSource_basic (20.24s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/identitystore      31.620s

[github-actions]

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[liath]

I went with the arrays of each result attribute style from ssm_parameters_by_path vs one array for each result like they come from the API (ala iam_access_keys). Happy to switch if that wasn't the right call but I didn't see anything in the docs to prefer one over the other. I figured the majority of callers only care about the member_ids field anyways so we might as well make that as easy to consume as possible.

[liath]

Migrated to the plugin framework as @aristosvo has done for #31681 / #36993, hopefully that helps it get merged.

[jar-b]

LGTM 🎉

% make testacc PKG=identitystore TESTS=TestAccIdentityStoreGroupMembershipsDataSource_
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.23.7 test ./internal/service/identitystore/... -v -count 1 -parallel 20 -run='TestAccIdentityStoreGroupMembershipsDataSource_'  -timeout 360m -vet=off
2025/03/18 11:20:38 Initializing Terraform AWS Provider...
=== RUN   TestAccIdentityStoreGroupMembershipsDataSource_basic
=== PAUSE TestAccIdentityStoreGroupMembershipsDataSource_basic
=== CONT  TestAccIdentityStoreGroupMembershipsDataSource_basic
--- PASS: TestAccIdentityStoreGroupMembershipsDataSource_basic (8.91s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/identitystore      15.523s

[jar-b]

Thanks for your contribution, @liath 👍. I added handling for the member_id union type and some test checks.

[ewbankkit]

LGTM 🚀.

[github-actions]

Warning

This Issue has been closed, meaning that any additional comments are much easier for the maintainers to miss. Please assume that the maintainers will not see them.

Ongoing conversations amongst community members are welcome, however, the issue will be locked after 30 days. Moving conversations to another venue, such as the AWS Provider forum, is recommended. If you have additional concerns, please open a new issue, referencing this one where needed.

[liath]

Thanks @jar-b and @ewbankkit

As for #31688, I imagine that will need the same changes as this

[github-actions]

This functionality has been released in v5.92.0 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!