[xCluster/Tablet Splitting] Support tablet splitting for bootstrapping streams

[hulien22]

Jira Link: DB-2855

Description

Currently we disable tablet splits for any tables that have tablets that are in the INITIATED state. This is usually fine since the bootstrapping process shouldn't take too long. One potential issue here is that if a user initiates a bootstrap but never finishes setting up the full replication and don't clean up the INITIATED streams with delete_cdc_stream - in this case tablet splitting would continue being blocked until these streams get deleted.

To implement this, we need to do some work to handle bootstrap_cdc_producer and setup_universe_replication being called on a table with a different number of tablets. Currently setup will just start replicating from the current active set of tablets, but this leads to some issues as we wouldn't poll from any parent tablets that were split during the bootstrap process - leading to missing data + stuck metadata (as we won't clean up the parent streams from cdc_state). We either need to reconstruct the list of original tablets, or store that somewhere during the bootstrap call