Add Sidekiq execution Application SLIs to the Rails application

With this, we should make the application emit the following metrics:

• gitlab_sli:sidekiq_execution_apdex:total: incremented for every job that successfully finished
• gitlab_sli:sidekiq_execution_apdex:success_total: incremented for every successful job that completed fast enough based on it's urgency (https://docs.gitlab.com/ee/development/sidekiq/worker_attributes.html#job-urgency)
• gitlab_sli:sidekiq_execution:total: incremented for every finished job
• gitlab_sli:sidekiq_execution:errors_total: incremented for every failed job

All of these metrics should include the following labels:

• worker
• feature_category
• urgency