Enterprise connections - Manage SSO buttons on auth screens

STAGE: Done

You can create several auth experiences for enterprise connections:

(Existing) Seamless sign in - use home realm discovery for all enterprise connections. This hides the SSO buttons and silently authenticates users against the IdP.
(New) Universal button - add a universal SSO button to the auth screen. This requires users to explicitly click the button and then authenticate on a new screen. Works for single or multiple connections.
(New) Force SSO button - include an SSO button for each enterprise connection. Toggle this option on if you use home realm discovery.