[CBSE] Avoid stream rollback if only a few indexes require it

If rollback is required for one index using a stream, then it can lead to rollback of all indexes using that stream. This can be avoided if rollback is handled by a separate stream.

Specifically, Indexer can fetch the purge seqno from KV at the time of restart. If some of the disk snapshots have lower sequence number than the purge seqno, those can be reset to Created state.

The fix for MB-47544 can help simplify this scenario as well.