Merge branch 'add-sidekiq-stats-metrics' into 'master'

Add Sidekiq::Stats metrics

See merge request gitlab-org/gitlab-monitor!94
2 jobs for master in 51 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #4532681
rspec

00:00:51

passed #4532682
rubocop

00:00:47