Look into storing users separately in keycloak backup

[PGijsbers]

Currently keycloak configuration and users are backed up in the same file. I think it would be better to back them up separately. We want to be able to share configurations without sharing users. Or roll back either independently.

There is a function for that, but we are not yet sure how to recover the users after a backup. Would be worth looking into and changing the script accordingly.

Original discussion #286 (comment)