Addition of snapshot_metadata CLI

I want to add below CLIs:-
1. Set or Delete metadata on a snapshot
2. show metadata of a snapshot
3. show metadata of a volume
4. Update all metadata of volume
5. Update all metadata of snapshot

Examples about CLI and arguments:-
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cinder snapshot-metadata <snapshot> <action> <key=value> [<key=value> ...]

Set or Delete metadata on a snapshot.

Positional arguments:
  <snapshot> ID of the snapshot to update metadata on.
  <action> Actions: 'set' or 'unset'
  <key=value> Metadata to set/unset
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cinder metadata-show <snapshot>

Show metadata of given snapshot

Positional arguments:
  <snapshot> Id of snapshot
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