feat: add example project

[ewanharris]

Description

Adds an example for the JS SDK that copies the structure of the other SDKs. I made the following choices here:

• Usage of ESM instead of CommonJS - Personal opinion that we should be moving to this in documentation
• Usage of top level await/mjs - Avoids having to use an async iiife to allow using async/await
  • I think we could move to a .js file with a type field in the package.json of the example if desired
• No package-lock committed - It's just another file to maintain and keep in sync between the SDK repo and the generator repo, and realistically adds 0 benefit

These two choices are what primarily drove the require for the >=16.13.0 (earliest 16 LTS) value in the examples engines.node field, although there is no check here so earlier versions will error with a potentially unhelpful error (is it worth adding a check?).

References

Closes out #198
Generated from: openfga/sdk-generator#305

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