Add metrics to dynamo workers

Re-enabled the dynamo-rds synchronizer.  The load on RDS was mainly caused by extremely large offsets.  The worker takes more than 1 second to finish if the offset is near 1 million.  Whereas the worker's interval is 1 second, which is not long enough to finish on time.  So instead of randomly sampling one node every 1 second, sample 5 nodes every 5 seconds, which should eliminate the increased load on RDS.

Added latency and count metrics to the two dynamo workers.

Moved the dynamo update manager to the repository-managers package.