[session, repository] deprecate repo.connect and move .close reponsibility to session object
Repository.new_session just returns a plain session object, and
`.connect` (which returns a sessionid) is deprecated.
For .close::
session.close() # done !
The session will bear the responsibility to call the "session_close"
event but that's better than the previous idiom::
repo.close(session.sessionid)
which involves both objects.
Related to #1381328.
Related to #2919309.