feature: add TypeDefinitions proto

Add TypeDefinitions. This will allow us to read and output an array of type definitions using protojson.

Description

[ ] 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]
[ ] 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