Split sidekiq from rest of rails for SQL latency SLIs

We currently cannot meet the Rails SLI if we include Sidekiq (see gitlab-com/gl-infra/production#4326 (closed))

This approach splits out Sidekiq (primary + replica) into its own pair of SLIs for primary + replica, with a looser apdex threshold because background jobs do not have as tight requirements on how long queries can take for the UI to generally remain performant.