This commit refactors the login flow to a GTS server thanks to an update
in the official GTS documentation.
golang.org/x/oauth2 is no longer needed.
Documentation reference:
- https://docs.gotosocial.org/en/latest/api/authentication/
Add Enbas code. So far Enbas can:
- Allow the user to register the application and log into GTS on their
behalf. The scope is limited to read for now.
- Show instance details.
- Show local and remote accounts.
