Add a Mergetree Setting Use_minimalistic_part_header_in_zookeeper

Add a MergeTree setting use_minimalistic_part_header_in_zookeeper. If enabled, Replicated tables will store compact part metadata in a single part znode. This can dramatically reduce ZooKeeper snapshot size (especially if the tables have a lot of columns). Note that after enabling this setting you will not be able to downgrade to a version that does not support it. #3960 (Alex Zatelepin)