Add counters to track the activity of auditor and replication workers

Once we enable auto recovery, auditor and replication workers start their activity. Today there is no way to monitor it using counters. This is a bug to track various activities of auditor and replication workers like:

• Time taken by auditor to build the bookie->ledger list
• No. of under replicated ledgers detected
• Time taken by auditor to publish the under replicated ledger list
• Time taken by auditor to check all the ledgers in the cluster
• No. of ledgers replicated by each replication worker
• No. of entries and bytes of data read and written by each replication worker
• Auditor can also report the distribution of ledgers within the cluster: how many bookies own a piece of ledger, etc.