[schema2sql] More docstrings and minor API improvements Along the way, renamed local `column` variable to `attr` where we're NOT manipulating a DB column name but a schema attribute. Related to #14050899

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances