For certain setups we don't need the ADMIN_USER_ID to be set. It is
mainly needed for bootstrapping the internal idm and the initial role
assignment. If roles are assigned by other means (e.g. OIDC claims
in the future) we don't need it.
This makes the ADMIN_USER_ID optional, also if ADMIN_USER_ID is unset
we don't need to configure a password for the admin user. We will still
generated the admin_id and password when running 'ocis init', but it is
ok to run manual setups without those settings.
