Add instrumentation for count of deployment approvals

What does this MR do and why?

This merge request adds two metrics to count deployment approvals:

• 28d timeframe: usage_activity_by_stage_monthly.release.deployment_approvals
• all timeframe: usage_activity_by_stage.release.deployment_approvals

Resolves #361809 (closed).

How to set up and validate locally

1. Navigate to Admin Area > Metrics and profiling.
2. Under Usage Statistics, check the preview payload of service ping to see the new metrics.

MR acceptance checklist

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.