[ML] UnusedStateRemover will remove all state for jobs not in cluster state #37109
Description
The UnusedStateRemover only checks which jobs exist by looking in the cluster state. It deletes state documents that do not correspond to a job that exists. Therefore, following the move to storing job configurations in an index it will delete all model state for such jobs each night, leaving them unable to be reopened if they are closed before another background persist is performed.
The UnusedStateRemover needs to be changed to consider jobs in both cluster state and indices. (This basically means it should get the jobs list via the job manager - the problem is very similar to the one fixed in #36936.)