fix: allow usage of module and extend as identifiers

[ewanharris]

Description

Currently if extend or module are used anywhere as identifiers then they will cause a parse error, so add them to the identifiers list along with other keywords

References

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