logging_sender.py: permit to choose a matrix chan where to send the notification

[OniriCorpe]

The problem

• Autoupdater pushes it's notifications on yunohost-dev, where it's irrelevant, this notif is for packagers

The solution

• Permit to choose a matrix channel where to send the notification, so the tool is more versatile and the notifications are pushed to a chan where they're relevant

took inspiration here: https://github.com/YunoHost/webhooks/blob/master/server.py#L34

PR status

not tested
ready to review