Restart zero worker if there is still work to do (#18658) (#18672)

Restart zero worker if there is still work to do (#18658) (#18672)

* Restart zero worker if there is still work to do (#18658)

Backport #18658

It is possible for the zero worker to timeout before all the work is finished.
This may mean that work may take a long time to complete because a worker will only
be induced on repushing.

Also ensure that requested count is reset after pulls and push mirror sync requests and add some more trace logging to the queue push.

Fix #18607

Signed-off-by: Andrew Thornton <art27@cantab.net>
* Update modules/queue/workerpool.go