Add a worker for reporting global stats to Prometheus

Fixes #1789

data/model/user.py

@@ -643,6 +643,10 @@ def get_active_user_count():
   return get_active_users().count()
 
 
+def get_robot_count():
+  return User.select().where(User.robot == True).count()
+
+
 def detach_external_login(user, service_name):
   try:
     service = LoginService.get(name=service_name)