Implement setRoutingData for MetadataStoreDirectoryService #842
Description
setRoutingData was an endpoint that was defined but not finished. It allows users to overwrite whatever routing data there is for a namespace and replace it with a new set of data. This endpoint was designed with convenience in mind because it allows users to specify the routing data in one call instead of making multiple calls to create zkrealms and add sharding keys.
Originally, it was designed that this endpoint will validate the routing data provided by users. However, we have decided against that (related: #841 ). This is because getRoutingData is able to return invalid or incomplete routing data, such as one that includes a zkRealm with no sharding keys. setRoutingData should be able to use the response from getRoutingData without an error. Users will be notified in the manual that setRoutingData does not validate the routing data they provided, and they will be responsible for the validity.