feat: remove the unimplemented flag from UpdateStore request

[rhamzeh]

Description

This removes the unimplemented flag from the UpdateStore method.

Note: I would prefer that this becomes a PUT instead of a PATCH as it currently is, however will leave that up for discussion before contributing that change

References

Goes in tandem with:

Review Checklist

• [x] I have clicked on "allow edits by maintainers".
• [ ] I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• [x] The correct base branch is being used, if not main
• [ ] I have added tests to validate that the change in functionality is working as expected