[self-hosted] Empty login options

[aledbf]

Bug description

If there are no authProviders configured, the login doesn't show any action

Steps to reproduce

Expected behavior

A message indicating that there is no configured authentication provider?

Example repository

[AlexTugarev]

We need to reinstate a setup page for this case. It used to render the Git Provider component to allow you to setup and connect with a IdP. This is also the way the first user is created.

cf. #3893