Description of problem:
We need to provide an alert when Gnocchi queue is growing in our availability monitoring solution.

Use case:
As an operator, if the number of messages in my gnocchi queue keeps on growing, that's a clear indication that something is going wrong in my setup and I need to be notified of it

Satisfaction criteria:
- a check is implemented
- check are deployed for gnocchi
- alert are sent when queue is growing