Provide subset of shards for certain VReplication Commands

[rohit-nayak-ps]

Description

For clusters with large number of shards, when there are workflows which only have a few participating shards, like Partial MoveTables for example, there is a huge overhead when commands contact all primaries in a keyspace with most returning no results.

This PR adds a --shards option for the vtctlclient and the vtctldclient for

• the Workflow command so that Show, Stop, Start and Delete only operate on the specified shards.
• the MoveTables command (only for partial move tables) for all sub-commands except Create.

Note that we expect the user to know what they are doing since we don't validate that the specified workflows are not present on other shards and hence can result in only a few streams being updated and potentially cause data loss and cluster inconsistencies if this is done for SwitchTraffic for example.

Related Issue(s)

Fixes: #14204

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[rohit-nayak-ps]

Replaced by #14873