Add mwh sensor to CX MT service usage monthly DAG
Bug: T407934
The generation query of CX MT service monthly DAG is also dependent on MediaWiki history dataset (for deletion counts). However, as there is no sensor to wait for MediaWiki history snapshot, the DAG runs before the data becomes available, leading to empty output.
The MR adds a sensor for MediaWiki history partitions to become available before proceeding to generation step.