[service] drop the asynchronous execution possibility
Call_service was able of both sync and sync execution making the API confusing.
There is not user of the async case. We drop the async argument in favor of
synchronous execution only.
This makes call_service the official API to call server side code from the
client side. This is a remplacement for the usual monkey patching of the repo
object.
The zmq notification bus is a solid alternative for codes that needs to start an
async execution.
What's new in CubicWeb 4.0?
============================
API changes
-----------
* ``RepositorySessionManager.postlogin`` is now called with two arguments,
request and session. And this now happens before the session is linked to the
request.
* ``SessionManager`` and ``AuthenticationManager`` now take a repo object at
initialization time instead of a vreg.
* The ``async`` argument of ``_cw.call_service`` have been dropped. All call are
now synchronous. The zmq notification bus looks like a good replacement for
most async usecase.
Deprecated Code Drops
----------------------
* The ldapuser source has been dropped. ldapfeed is the only official source
remaining for ldap.
* session.hijack_user mechanism has been dropped.