Add a sync channels to monitor task processing

[gnuletik]

Quoting @yomguy

An implementation example of a notification system using django-channels:

https://realpython.com/getting-started-with-django-channels/

Quoting @gnuletik

IMO the challenge is how can we implement this progression on the API's async task (transcoding, analyzing) rather than how to do it with Django. But that's good to keep this nice resource :)

See Ircam-WAM/timeside-player#89

Also linked to the task notification workflow : #193