feat(storage): improve clarity of offline garbage collection log output

mentioned in commit 0c547058

mentioned in issue #683 (closed)

mentioned in merge request gitlab-org/build/CNG!1027 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1801 (merged)

mentioned in merge request gitlab-org/charts/gitlab!2580 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1802 (merged)

mentioned in merge request omnibus-gitlab!6181 (merged)

mentioned in merge request gitlab-development-kit!2656 (merged)