List Google Play testing tracks, create a closed testing track, and attach Google Group tester lists via the Android Publisher API

Documented steps

1. POST .../applications/{packageName}/edits (edits.insert) and capture editId.
2. GET .../edits/{editId}/tracks (edits.tracks.list) to enumerate every Track resource, including tracks with no releases.
3. GET .../edits/{editId}/tracks/{track} (edits.tracks.get) for one track. Default identifiers are 'production', 'beta' for open testing and 'qa' for internal testing; closed testing tracks carry custom names.
4. To create a closed testing track, POST .../edits/{editId}/tracks (edits.tracks.create) with a TrackConfig body. All three fields are required: {"track":"my-closed-track","type":"CLOSED_TESTING","formFactor":"DEFAULT"}
5. FormFactor values are FORM_FACTOR_UNSPECIFIED, DEFAULT, WEAR, AUTOMOTIVE. Use DEFAULT for a phone/tablet track.
6. Configure the release on that track: PUT .../edits/{editId}/tracks/{track} with {"track":"qa","releases":[{"versionCodes":["123"],"status":"completed","releaseNotes":[{"language":"en-US","text":"Bug fixes"}]}]}, or edits.tracks.patch for a partial update.
7. For form-factor tracks, prefix the identifier, e.g. wear:qa or automotive:production.
8. GET .../edits/{editId}/testers/{track} (edits.testers.get) to read the current Testers resource for that track.
9. PUT or PATCH .../edits/{editId}/testers/{track} (edits.testers.update / patch) with {"googleGroups":["testers@yourdomain.com"]} to set the tester groups.
10. POST .../edits/{editId}:commit to make the track, release and tester changes live.