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