domain: make app_id construct only
domain: make app_id construct only

We can't really change this as it is currently implemented,
so we better reflect this for now.

https://phabricator.endlessm.com/T16339

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib