More team members should have permissions to release package.

[polina-c]

dart run tool/release/bin/release.dart publish --force fails for most team members:

Message from server: `polinach@google.com` has insufficient permissions to upload new versions to existing package `genui_firebase_ai`.
Failed to publish genui_firebase_ai

We need to add steps to get permissions to either CONTRIMITING.md or go/flutter-genui-internal

[polina-c]

@yjbanov , can you check if you have permissions?

[parlough]

Just as a note, a more long-term flexible solution might be to set up automated publishing to pub.dev. There's package:firehose which provides some extra PR checks and tooling around it in multi-package workspaces.

[polina-c]

Context: we have bumped version, but we do not have permission to publish it.

[polina-c]

Emailed 'how to publish to labs.flutter.dev' to dart ecosystem team.