ShardCatalogHistoryCleanup is a component in charge of cleaning up stale, unreachable, unowned chunks that were preserved to support PIT reads.

There are some caveats about the current implementation:

1. Serialization with chunk operations
2. Serialization with DDLs
3. Inconsistent state about collection entries and chunks

We need to rewrite it in a simpler way that ensures the cleanup job modifies the shard catalog consistently, as the current implementation does not guarantee that.

This cleanup job only impacts performance in situations where, upon refreshing from disk, the shard has a large number of unreachable unowned chunks on disk. In any case, this is necessary for durability and correctness.