supervisor-xqueue: Move xqueue & xqueue_consumer to supervisord
supervisor-xqueue: Allow to override `LANG` for xqueue
supervisor-xqueue: Run the xqueue processes as `common_web_user`

supervisord as well as all the processes it controls are run as
`{{ common_web_user }}`. This allows us to connect to it as that
user which allows us to manage the processes as www-data, instead
of root.
supervisor-xqueue: Reload supervisord immediately after adding config files

To ensure they are taken into account before we try to start the process
through supervisord.
supervisor-xqueue: Use `{{xqueue_venv_bin}}` instead of `{{xqueue_venv_dir}}/bin`