feat(cloud monitoring): add support for cloud monitoring suppressions

This adds support for Cloud Monitoring suppressions.

It provides a couple of basic functions:
- getEntities to list all entities on your account,
- getEntityIdsByRegexp to get all the entity ids whose label matches a specific regexp (useful when entity labels are set to server hostnames and you want to get i.e. all your api servers or all your servers in a region)
- createEntitiesSuppression to create a suppression on an array of entity ids,
- deleteSuppression to delete a suppression.
You can suppress an entity with as many suppressions as you want, it is perfectly legal. Any suppression currently valid applying to an entity will suppress its alarms.

You might have, for example, a suppression for your api servers and another for one region. In this case there are two suppressions for the api servers of that region. This is fine.