Add default Idp to switch to when domain not found within email domains from IdP

[egeorges92]

The goal is to set a default IdP in case no IDPs respond to the user's email domain.
PR to follow

[egeorges92]

PR : #398

[sventorben]

This has been discussed before and can be achieved with KC out of the box. See this thread for example: #34 (comment)

Therefore, I will probably not implement and maintain it.

[sventorben]

Getting the discussion back to this thread.

From #34 (comment)

Thank you, Sven, for the tipr.
I try before the Identity Provider Redirector. The issue with it, is that it doesn't sent the login_hint to the IdP, and it's an essential requirement for my use case.

That is a totally different thing. Probably I am not setting the login hint session attribute properly in that case. I am using the exact same logic as Keycloak does for the redirect. So I assume that in case no home IdP can be found, I am not setting the login_hint.