Move active_users_project_repo metric to Snowplow

Closes https://gitlab.com/gitlab-org/product-intelligence/-/issues/539

In https://gitlab.com/gitlab-org/product-intelligence/-/issues/493 we selected experimental set of metrics. Now we need to send them using Snowplow.

Metric usage_activity_by_stage_monthly.create.action_monthly_active_users_project_repo is an HLL metric which is time grouped monthly