Summary:
Added the following wait events for ASH Instrumentation of snapshots:-

1. Snapshot_WaitingForFlush :- A snapshot operation is waiting for a RocksDB flush.
2. Snapshot_CleanupSnapshotDir :- A snapshot operation is cleaning the snapshot directory.
4. Snapshot_RestoreCheckpoint :- A snapshot operation is restoring a database checkpoint.
5. RocksDB_CreateCheckpoint :- RocksDB is creating a database checkpoint.

We also add a new query id for Snapshot wait events (QueryIdForSnapshot).
Jira: DB-12143

**Upgrade/Downgrade safety:**
The additional fields are optional and it should not cause an issue if they are missing, only the
ASH metadata will be incorrect, which is fine during the upgrade/downgrade phase.

Test Plan: ./yb_build.sh --cxx-test wait_states-itest

Reviewers: hbhanawat, mhaddad, amitanand, atharva.kurhade

Reviewed By: mhaddad, amitanand

Subscribers: yql, ybase

Differential Revision: https://phorge.dev.yugabyte.com/D43915