feat(model): run tests against a built-in OpenFGA engine

[rhamzeh]

Description

• Update README
• Decide on whether to keep remote option
• Update the OpenFGA dependency once fixed upstream

Notes:

• Complex examples with > 20 contextual tuples won't run against remote engines b/c contextual tuples > than the limit.

References

• Closes Run tests against a built-in OpenFGA engine instead of requiring a remote engine #141

Testing

1. Clone this branch
2. Run make build
3. Run ./dist/fga model test --tests example/tests.fga.yaml

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