[Snapshot] Finish TestOMSnapshotDAG, restore CompactionNode SnapshotID field for debugging

Finish up left over items from HDDS-7281:

1. Fully implement the integration test TestOMSnapshotDAG – in order to run the test efficiently, add a new config to tune DB write buffer will be added to ozone-site.xml (the cleanest way to implement that I can think of atm. We can potentially add much more DB tunables to Ozone config xmls once snapshot branch is merged to master)
2. Restore CompactionNode SnapshotID field functionality for easier debugging
3. Optimization: Activate listener (attached already) only after the first snapshot is taken – It looks like SnapshotChain is not put into use yet. I will wait for that to more efficiently get snapshot count (if zero, skip DB listener and pause the SST backup / compaction log appending)