Implement getAllMappingUnderPath and getMetadataStoreRealm for ZkMetadataStoreDirectory #750
Description
Methods getAllMappingUnderPath and getMetadataStoreRealm in ZkMetadataStoreDirectory were not previously implemented because they were dependent on TrieRoutingData, which has now been finished. Also, ZkRoutingDataReader has some logic changed in getRoutingData; in particular, not having realm addresses and not having sharding keys for some realm addresses no longer raise exceptions.