release-22.1:Backport!6379

Merged Andrey Vertiprahov requested to merge cherry-pick-f0db95b1 into release-22.1

Add task_stale_count metric to selfmon.

See merge request !6379 (merged)

(cherry picked from commit f0db95b1)

56d02ac1 Add task_stale_count metric to selfmon.

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