Add memory killer running jobs to prometheus

What does this MR do and why?

Adds Prometheus counter metric for running jobs, when SidekiqMemoryKiller is above Prometheus metric: sidekiq_memory_killer_running_jobs labels: worker_class, deadline_exceeded

Example:

sidekiq_memory_killer_running_jobs{deadline_exceeded="false",worker_class="UpdateAllMirrorsWorker"} 277

Screenshots or screen recordings

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

related_to: #368513 (closed)