Support managing ClusterPools

[KevinFCormier]

Similar to the cm new and cm delete commands which act as a frontend for simplified usage of lifeguard/clusterclaims scripts, we may want to include cm new-pool and cm-delete-pool commands, and perhaps even more useful, cm set-pool-size.

cm set-pool-size could be useful in a cronjob to automatically scale up pools during periods when users are likely to need new clusters.

For the new/delete commands, would need to consider if we should require a pre-existing CLOUD_CREDENTIAL_SECRET to be defined. The name of this secret could be shared in the squad's configuration file, and where possible, the credentials could belong to a functional ID. Other provider specific options such as region/domain would be safe to share widely as well.