Fixes #6952 - Set hostgroup after provisioning from pxe

After hostgroup provisioning, when the machine has registered
with foreman, it should be in the same hostgroup.
to achieve this behavier, the fact foreman_hostgroup should be
added to hostgroup provisioning template

Fixes #13775 - merge if data set is present

Fixes #17525 - Add a friendly error message to invalid dns_id

Fixes #17257 - Allow specific configs to be recreated

Fixes #17503 - Only trigger PXELoader suggestion when needed

Previously every host instantiation triggered a PXELoader suggestion,
which led to up to 3 extra queries per host loaded. This changes so that
the suggestion is only applied when a host changes it's OS.

Fixes #17548 - Orphaned smart class parameters are hidden

Fixes #17487 - support sessions for api calls

- authenticated api calls save user to session and set
flag api_authenticated_session
- sessions with such flag allow posting requests without CSRF token
- api sessions exipre the same way as UI sessions
- api sessions don't store any additional data to keep the requests...

Refs #1556 - Remove puppet docroot setting from db and tests

Fixes #17483 - async task creation returns 202

Includes task link in response

Fixes #15779 - make background processing available