[Segment Replication] Merge to main tracking issue - Checkpoint publishing.

[mch2]

This is a tracking task for the steps in merging Checkpoint publishing back to main. These new components do not need to be wired up yet within IndexShard.

• New CheckpointRefreshListener class ,
• SegmentReplicationCheckpointPublisher class
• New TransportReplication action class - PublishCheckpointAction.