admin/plugin: delete job_detail files when jobs are pruned from memory (#8722)

* admin/plugin: delete job_detail files when jobs are pruned from memory

pruneTrackedJobsLocked evicts the oldest terminal jobs from the in-memory
tracker when the total exceeds maxTrackedJobsTotal (1000). However the
dedicated per-job detail files in jobs/job_details/ were never removed,
causing them to accumulate indefinitely on disk.

Add ConfigStore.DeleteJobDetail and call it from pruneTrackedJobsLocked so
that the file is cleaned up together with the in-memory entry. Deletion
errors are logged at verbosity level 2 and do not abort the prune.

* admin/plugin: add test for DeleteJobDetail

---------

Co-authored-by: Anton Ustyugov <anton@devops>
Co-authored-by: Chris Lu <chris.lu@gmail.com>

weed/admin/plugin/plugin_monitor.go

@@ -1134,7 +1134,11 @@ func (r *Plugin) pruneTrackedJobsLocked() {
 	}
 
 	for i := 0; i < toDelete; i++ {
-		delete(r.jobs, terminalJobs[i].jobID)
+		jobID := terminalJobs[i].jobID
+		delete(r.jobs, jobID)
+		if err := r.store.DeleteJobDetail(jobID); err != nil {
+			glog.V(2).Infof("Plugin failed to delete job detail for pruned job %s: %v", jobID, err)
+		}
 	}
 }