feat: use and authentication and authorization server

[guenhter]

Integrating Basic Auth, OIDC, SAML, ... into the app is not funny and time consuming.
Luckily there are ready to use solutions:

• Keycloak
• Authelia
• Zitadel
• casdoor
• supertokens
• Logto
• NextAuth
• authentik
• ...

Analyse them and integrate one of those instead of implementing OIDC, SAML, ... direclty

[guenhter]

Authentication is done: only OIDC is possible now. IDPs like Zitadel can be used then to do the auth (even Username/Password based). So modAI completely hand off the Authentication to the IDP and only needs to maintain OIDC (and here only support one single OIDC connection)

[guenhter]

Authorization is still an open topic.