Add probe_jobs_limit probe for Sidekiq
This does the same as #probe_jobs, but only looks at the first PROBE_JOBS_LIMIT jobs in each queue. This means that we run a single LRANGE command for each queue, which does not block other commands. For queues over PROBE_JOBS_LIMIT in size, this means that we will not have completely accurate statistics, but the probe performance will also not degrade as the queue gets larger.
DO NOT USE this and probe_jobs together, as they export the same metric (sidekiq_enqueued_jobs).
Edited by Sean McGivern