cubicweb #4723580 provide an utility to get a working cnx with admin creds from an app id [validation pending]

e.g.::

cnx = admincnx('babarinstance')
with cnx:
babar = cnx.find('Elephant', name=u'Babar').one()
babar.kill()
cnx.commit()

prioritynormal
typeenhancement
done in3.20.0
load0.100
load left0.000
closed by#78ab2b14048a [utils] provide a function to return an admin connection from an appid
patch[utils] provide a function to return an admin connection from an appid [applied]