Discover endpoints and sidekiq jobs that are CPU-intensive
Following the https://gitlab.com/gitlab-org/gitlab-ce/issues/62876#note_190720305
We should have an automated way to discover all endpoints that are CPU-bound and gonna cause the problem when running on Puma.
We should introduce Prometheus metrics/histogram that would measure real-time spend when executing CPU thread, PROCESS_THREAD_CPU_TIME
and include that in our dashboards to ask for optimization and prioritization.
This is to make Puma to work predictable, as today single request can hog the execution and introduce hard to discovery latency problem when running on Puma per comments in https://gitlab.com/gitlab-org/gitlab-ce/issues/62876#note_190720305.
Examples of such endpoints: