feat: storage sharding schema for marconi-queues

This provides a base jsonschema for handling PATCH and PUT requests to
a future /v1/shards/{shard_name} endpoint.

Change-Id: I10c817ff8b5c196a2a3b2f5562e1bafc34e30adf
Partially-Implements: blueprint storage-sharding
Merge "feat: storage sharding schema for marconi-queues"