ENG-4492: Separate EE hashinator update from partition count change in site.
ENG-4492: Change the constructor of SnapshotSiteProcessor to take a site tasker
queue instead of a runnable that wraps around the site tasker queue.
ENG-4492: Add per-site post-snapshot task to the SnapshotSiteProcessor.

These tasks will be run on each site after all snapshot serialization tasks are
finished but before the snapshot transaction ends.
ENG-4492: Create post-snapshot tasks for stream snapshot if requested.
ENG-4492: Make a snapshot request JSON string that may include post-snapshot
tasks for elastic join.
ENG-4492: Refactor the snapshot interest in the JoinerProducerBase so that it
can be used to monitor more than one snapshots in sequence.
ENG-4492: Add blocking partitioned table data transfer to the
ElasticJoinProducer.