Allow "simple" OIDC setups for self-hosted instances

Hello!

Is it possible to change the OIDC setup to be “normal”, as in:

• No domain restrictions (anyone can login using OIDC)

• No implicit routing to OIDC providers

This would go towards the more common implementation of OIDC sign in, where the security layer is the OIDC provider, and not the application (with domain routing).

This would also imply a change in the login screen, because you’d need to have, like most apps do, two login methods side-by-side — email/password and OIDC providers. With the option to disable password login, if the instance admin only wants OIDC login available.

I am willing to help with a PR for this, if the team is open to it! :)

Thanks!