Improve docs on how to revert the initial set OCIS_ADMIN_USER_ID

[JoFeKW]

The customer was looking for a way to revert the right set using the initial set OCIS_ADMIN_USER_ID.

This can be done via WebUI/API.

Switch to role provisioning is possible via OIDC if needed

@wkloucek

[wkloucek]

Background:

Whenever a user, whose ID is configured in OCIS_ADMIN_USER_ID logs in, the user is configured to have the admin role.

When the ID configured in OCIS_ADMIN_USER_ID is changed, the previously logged in user DOES NOT loose the admin role. Another admin user could still change the user role of that user via WebUI or API.

From my point of view, this is the expected outcome and only needs to be reflected in the documentation.

If role changes should be dynamically managed, OIDC role provisioning is the way to go.