[ADD] monitoring_prometheus_queue_job

This commit features a refactoring of monitoring_prometheus to get a
cron gathering some metrics from the database, and then publishing the
result on the /metrics endpoint

The new module monitoring_prometheus_queue_job extends the cron to get
information about the queue job states.

monitoring_prometheus/security/ir.model.access.csv

@@ -0,0 +1,2 @@
+id,name,model_id:id,group_id:id,perm_read,perm_write,perm_create,perm_unlink
+access_prometheus_metric_system,prometheus.metric system,model_prometheus_metric,base.group_system,1,1,1,1