backup entire Zookeeper state for a table

if anything on Zookeeper goes wrong we can't recover the state.

- Pinot needs a way to backup entire zookeeper state (in consistent fashion) for a table so it would be able to recover it.
- Pinot should also validate a backup and only declare the backup valid if all deep store files referred exist

No files or tests are identified. Start by locating how Pinot stores a table's state in ZooKeeper and records referenced deep-store files; then determine the existing entry points for backup and recovery. Done means a consistent table-state backup can be validated against all referenced deep-store files before being declared valid.

Written by the indexing model from the issue text.