Add global_search_indexing to sidekiq service

This will add the global search apdex indexing SLI to the Sidekiq service in the runbook. I followed these steps: https://docs.gitlab.com/ee/development/application_slis/#using-the-sli-in-service-monitoring-and-alerts

part 1: !4996 (merged)

Current apdex ratio in Thanos

+- 99.6% over the last 2 days

Relates to gitlab-org/gitlab#372719 (closed)