feat(handlers): enable migration mode to be paused

mentioned in commit 6917f118

mentioned in merge request gitlab-org/build/CNG!740 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1139 (merged)

mentioned in merge request omnibus-gitlab!5542 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1142 (merged)

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