This ticket covers the upgrade/downgrade work in the design spec. It should include writing the history on upgrade and deleting it on downgrade, plus synchronizing the FCV change with any concurrently running move/split/merge operations. It is acceptable to block these operations while the upgrade/downgrade is running, but ideally that blocking should be limited on a per-collection basis and not globally.

As part of this ticket we should also make the shards and config server reject atClusterTime requests under FCV 3.6 and also that the ChunkManager::getCollectionRoutingInfoAt call will fail if it contains no history.