[server] replace repository's tasks manager by a scheduler Repository() does not accept anymore a 'tasks_manager' argument but rather a 'scheduler' argument which is expected to be an instance of sched.scheduler class. The drop the _tasks_manager attribute of the repository and adjust all internal usages of it. In particular, in the 'repo_stats' service we do not export 'looping_tasks' statistics anymore as there's no way to retrieve this anymore from a web instance. Closes #17057223.

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