Update README with MCPs and API Gateway details

[aaguiarz]

Added new MCP resources and updated API Gateway section.

Description

What problem is being solved?

How is it being solved?

What changes are made to solve it?

References

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