feat(datastore): add database row count metrics with distributed locking

mentioned in merge request gitlab-org/charts/gitlab!4494 (merged)

mentioned in merge request gitlab-org/build/CNG!2630 (merged)

mentioned in merge request omnibus-gitlab!8689 (merged)

mentioned in issue #1677 (closed)

mentioned in merge request gitlab-development-kit!5232 (merged)

mentioned in merge request omnibus-gitlab!8696 (closed)

mentioned in merge request omnibus-gitlab!8697 (merged)