cubicweb #2807739 transform call_service into a simple synchronous in-process (still appobject based) Repository extension mecanism [validation pending]

Let's give it a proper name ("repo-method"), as in::

vreg['repo-method'].select('wipe-all-caches', butnot=('querycache',))

prioritynormal
typeenhancement
done in3.19.0
load0.400
load left0.000
closed by<not specified>