Examine the logging we added for Shard Merge and remove messages we no longer need, or lower their severity. The goal is to reduce the volume of messages in Lobster that aren't helpful for diagnosing BFs, and reduce the volume of messages in Cloud log files that aren't helpful for diagnosing production issues.

TenantFileCloner is especially logorrheic, it doesn't need to announce every file and every batch of every aggregation cursor.