Feature Request: VStream API to dynamically include/exclude shards without tablets

[twthorn]

Feature Description

Add ability for vstream to support streaming data from a keyspace where some shards have zero tablets. In addition, if a shard then gets new tablets, the vstream should include the shard that now has tablets and can stream binlogs.

Slack thread

Use Case(s)

The use case here is for keyspaces where tablets are not guaranteed in every shard. This happens for some very large keyspaces. See slack thread for more details. Also in the case where a vstream consumer wants to keep up to real-time as much as possible even if some shards don't have tablets available, and wants to dynamically include them as they become available but not block on every shard being healthy.