Follow-ups of automated teams management from OIDC and SCIM

High priority:

• SCIM server integration (lib/Service/ScimService::fetchCircles()) still needs to be tested against a real SCIM server, and adjusted as needed once access is available
  • Waiting on reply from Helmholtz regarding access to a SCIM test server

Nice to have:

• Federation agent currently is created with CFG_BACKEND only
  • Maxence suggested creating it with CFG_APP + CFG_SYSTEM instead
  • Note: I think using CFG_APP would break some parts of this feature. IIRC, I attempted to set it at some point but ran into some issues, have to check again
• On frontend, when a SCIM circle has members from other instances, federation agent also appears there as a member
  • Would be nice to now show fedaration agent as a member, since it's a internal thing
  • Maybe we could add a CFG_FEDERATION_AGENT and set this config when creating federation agent
  • This way we could filter it out on frontend
• Add mechanism to allow user to disconnect from OIDC server.
• Consider setting the source of SCIM-created circles to "SCIM" instead of the current value.
• In lib/Service/FederationAgentService::ensureModerator(), if the federation agent is already a member but not a moderator, its level should be updated instead of being skipped