Count approval project rules metrics

What does this MR do and why?

Adds service ping for count of approval project rules configured.

How to set up and validate locally

1. Add an approval rule https://docs.gitlab.com/ee/user/project/merge_requests/approvals/rules.html#add-an-approval-rule

2. Verify data by running below script

 payload = ServicePing::BuildPayload.new.execute
 puts payload["usage_activity_by_stage_monthly"]["govern"]["approval_project_rule"]
 puts payload["usage_activity_by_stage"]["govern"]["approval_project_rule"]

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #382739 (closed)