Verify metric - CI Builds 28D (event-based)

Background

This is a request for the Verify team to instrument an equivalent, event-based, monthly (28D) metric for usage_activity_by_stage_monthly.verify.ci_builds that can measure "Total monthly (28D) CI Builds in Gitlab repositories for all project and project types" as that does not exist today.

Intended Use

This metric will be added to the current CI Adoption Score criteria (Epic: gitlab-com/sales-team/field-operations&254 (closed)), replacing Deployments metrics that currently sway the score heavily towards CD.

Proposal

Add a new metric definition via command line helper with the details above. Additionally, we'll need to add a new Metric instrumentation.