Adds CI Platform Metrics bookkeeping worker

**app/workers/all_queues.yml:**

- Automatically updated.

**app/workers/ci_platform_metrics_update_cron_worker.rb:**

- Adds a cron worker to update the CI Platform Metrics.

**config/initializers/1_settings.rb:**

- Cron settings for the new worker.

**spec/workers/ci_platform_metrics_update_cron_worker_spec.rb:**

- Spec tests for the new cron worker.

**config/gitlab.yml.example:**

- Adds cron settings to example config.