User account overview

[TheSlimvReal]

As an manager I want to have an overview over all user accounts that can access the app in order to manage permissions

After #2132 it will be possible for entities to be linked with Keycloak user accounts. This means user accounts will not only be linked to User entities and therefore wont appear in the "Users" tab. Instead we probably need a tab that shows all users registered in Keycloak for this realm, together with information like "email", "enabled", "email".

This could then even be extended with info like "last login", "2fa enabled", ...

Clicking a user should then probably show the UserSecurityComponent to allow the manger to make changes to the account. There should also be a link to the entity (e.g. User or Child) this account is linked to. So kind of the other way round as we currently do it.