docker: Improve swh-scheduler-schedule-recurrent service startup
requested to merge anlambert/swh-environment:docker-schedule-recurrent-service-improvements into master
In order for the origin loading tasks resulting from a listing to be successfully scheduled by that service, the loading task types must have been registered in the scheduler database prior the execution of the main command of that service.
So make the service depends on the swh-loader one and use a Python script to check the celery worker used to execute loading tasks have been started.