This adds support for authentication using a SSH certificate and normal public keys when you've got an ssh-agent running that has this certificate or your public key loaded.
First question when creating a new login is to ask about the ssh certificates or public keys, when the answer is yes, we don't need to ask about tokens/usernames anymore.
Co-authored-by: Wim <wim@42.be>
Reviewed-on: https://gitea.com/gitea/tea/pulls/442
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: 6543 <6543@obermui.de>
Co-authored-by: Wim <42wim@noreply.gitea.io>
Co-committed-by: Wim <42wim@noreply.gitea.io>
