[session] don't silently ignore commits commits while in the precommit or postcommit phase are silently ignored. This is OK in precommit since there'll be a commit afterwards anyway; OTOH in postcommit it may surprise the developer who didn't read the documentation for postcommit operations carefully enough. Related to #4383922.

usr/bin/cubicweb-ctl usr/bin/
usr/lib/PY_VERSION/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl