Add sidekiq_job_attempt_threshold config variable

The same idea as Tadas Tamosauskas's commit, but implemented differently and for Sidekiq. I am happy to make whatever changes you'd like.
My other concern is that this would cause the notice to be ignored if *any* parameters include a `retry_count` key which is over the threshold. Unlikely edge case, but I think it's another reason to keep this kind of thing specific to the Sidekiq integration rather than checking it here.