Digital hackerspace: integrate doorrequestservice with HaSpMan

Since our user management is now done in [HaSpMan](https://github.com/Brixel/HaSpMan), and the IdP is Keycloak, we no longer need OpenLDAP.

It should be possible to assign the right to use the "Door" to a user in HaSpMan, and still leverage the power of a local-only approach to open the door. This will still be the biggest challenge: creating a hybrid application, where HaSpMan is running on a cloud, on the public internet, while this service should still be working on the local network only.

No files, tests, or entry points are named. Start by mapping the current DoorRequestService authentication and door-opening flow, then review how HaSpMan and Keycloak expose user rights. Done means users can receive the Door right through HaSpMan while door access continues to work on the local network without OpenLDAP.

Written by the indexing model from the issue text.