[repository] add an ``internal_cnx`` method to replace ``internal_session`` Accessing the repo through a Session is deprecated. We need an easy replacement for ``internal_session``. This API change was a good occasion to stop disabling integrity hook by default. This is huge source of bug in user-code. related to #2503918

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"""cubicweb-%(cubename)s application package

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%(longdesc)s

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"""