SSO auto redirect

Problem

When SSO is required in cases where self-hosters want to centrally manage accounts, people visiting Fluxer always have to press the button of "Login with SSO". There is nothing else to do on this page, and just wastes a click from the user.

Proposal

Have a checkbox that makes users automatically be redirected to SSO login. This can make accessing Fluxer for users already logged in with their external IdP instant and seamless. It also removes the potential confusion users might have when they think they need to use their official Fluxer account to login on self-hosted instances (which I've been having a lot with my users).