Remove client_id/client_secret query parameter usage from GitHub API authentication

Remove client_id/client_secret query parameter usage from GitHub API authentication

Fix https://gitlab.com/gitlab-org/gitter/webapp/-/issues/2442

• https://developer.github.com/changes/2020-02-10-deprecating-auth-through-query-param/
• https://developer.github.com/changes/2019-11-05-deprecated-passwords-and-authorizations-api/#authenticating-using-query-parameters

Testing strategy

1. Start the app with debugging for the GitHub public token pool enabled -> for macOS/Linux: DEBUG=gitter:app:github:public-token-pool npm start, for Windows: set DEBUG=gitter:app:github:public-token-pool&&npm start
2. Paste a GitHub commit link in one of your rooms, ex. https://github.com/gitterHQ/sidecar/commit/ae2e261d86b8f0d2cc2fb3c92fb3a7e7c6f92617
3. Open an incognito browser and view the room
4. Hover the decorated commit link and notice you can see the content for the commit as well as github.anonymous.access logged in the CLI window for the server

Todo

• Update tentacles
  • https://gitlab.com/gitlab-org/gitter/tentacles/-/merge_requests/9
• Fix request-http-cache
  • https://gitlab.com/gitlab-org/gitter/request-http-cache/-/merge_requests/14