feat: (configurable on/off) if there is only one login provider, bypass the login page

[ericfitz]

Enterprise scenario - if you have exactly one login provider, then try to log on automatically

Needs a configurable setting with 3 states

• "disabled" - current behavior
• "landing" - on home page (/), "get started" should bypass login provider selection and just try to log you on, failing back to login provider screen
• "auto" - just navigating to home (/) should just try to log you on, failing back to login provider screen

[ericfitz]

Should be able to be enabled/disabled via a setting.