feat(gc): add dangling and event labels to online GC run metrics

mentioned in commit 8a8a2f12

mentioned in issue #531 (closed)

mentioned in merge request gitlab-org/build/CNG!836 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1397 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1402 (merged)

mentioned in merge request gitlab-org/charts/gitlab!2302 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1407 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1409 (merged)

mentioned in merge request omnibus-gitlab!5827 (merged)

mentioned in merge request gitlab-development-kit!2385 (merged)