feat(handlers): enable pre-imports via the Gitlab V1 API

mentioned in commit 3114d414

mentioned in issue #569 (closed)

mentioned in merge request gitlab-org/build/CNG!869 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1473 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1480 (merged)

mentioned in merge request omnibus-gitlab!5899 (merged)

mentioned in merge request gitlab-development-kit!2421 (merged)