Bug 32992: Move background_jobs_worker to misc/workers

Bug 32992: Move background_jobs_worker to misc/workers

On bug 32594 we are adding a new worker, dedicated to Elastic indexing.
We should have a common place for workers, and we agreed on misc/workers

To test:
1 - Apply patch
2 - reset_all in koha testing docker
3 - ps aux | grep background
4 - Confirm the workers are running, and running in the new directory
5 - Perform a batch item modification
6 - Ensure the job is processed by the worker

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>