feat(java-sdk): Adjust sdk-generator to be compatible with java-sdk

[piotrooo]

Description

I started working on openfga/java-sdk#127, but I realized that the java-sdk repo contains manually changed files not generated through the sdk-generator. This leads me to first align the code between the sdk-generator and the java-sdk.

Tip

I also believe that to prevent such modifications, all *-sdk repos should be set to read-only mode. As outlined in the contribution guides, all changes should be made thought the sdk-generator. As a very fist step, a GitHub Workflow could be introduced to manually generate SDKs.

Review Checklist

• 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

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: piotrooo / name: Piotr Olaszewski (b0493b2, e3153c5)

[piotrooo]

@rhamzeh can we merge this and go to java-sdk and generate code?

[rhamzeh]

Yes! Thanks for your PR and putting this effort @piotrooo!