feat: allow to just input service to sso login

[Decodetalkers]

No description provided.

[Decodetalkers]

Some service allow user to use sso login, like matrix.org and mozilla.org, sometime I do not want to remember my matrix id, it sometimes difficult for me to remember, and sso do not need them

[Decodetalkers]

@LorenDB cc, if use sso, the password and id is not needed , so I think this area is needed to be always visible

[deepbluev7]

You can actually currently enter any arbitrary user id to start sso with the respective server. I'm not sure if always showing that field is a much better solution, since it is at the bottom, usually doesn't need to be touched and the other fields are redundant in that case. It probably needs a different screen instead.