Support alternate names for ceph-fs charm and associated storage class

[addyess]

Overview

When the ceph cluster charm ceph-fs is deployed with an alternate application name, (eg ceph-fs-alt) the output after querying the cluster was an unexpected response.

ceph fs ls

[{
  "name":"ceph-fs-alt",
  "metadata_pool":"ceph-fs-alt_metadata",
  "metadata_pool_id":5,
  "data_pool_ids":[4],
  "data_pools":["ceph-fs-alt_data"]
}]

This led to needing to redesign for situations where there may be multiple ceph-fs pools, and the ability to create multiple storage classes based on the pool structure -- while maintaining that if theres is only one pool, it's name still resolves to cephfs

Details

• a new config cephfs-storage-class-name-formatter allows the charm admin to format the CephFS storage class name based on some context variables.
• the context provided to the CephFS Manifest is significantly revamps to support this more complete filesystem pool listing
• Increase the error checking for situations where the formatter isn't detailed enough to provide unique storage-class names

[bschimke95]

LGTM