Add DOCKER_SNAPSHOT_SUFFIX to help repos with "nested" docker images

Make it possible to reference the image from another instance of the component like so:

see: sylva-projects/sylva-elements/container-images/kube-job!277 (merged)

  - component: $CI_SERVER_FQDN/sylva-projects/sylva-elements/ci-tooling/ci-components/docker-build/docker-build@add-snapshot-suffix-variable
    inputs:
      as: kube-job docker
      target-platform: "linux/amd64,linux/arm64"

  - component: $CI_SERVER_FQDN/sylva-projects/sylva-elements/ci-tooling/ci-components/docker-build/docker-build@add-snapshot-suffix-variable
    inputs:
      as: kube-job-backup docker
      target-platform: "linux/amd64,linux/arm64"
      build-extra-needs:
        - kube-job docker-build
      registry: $CI_REGISTRY_IMAGE/backup
      dockerfile: Dockerfile-backup
      docker-build-args: >-
        --build-arg BASE_IMAGE=${CI_REGISTRY_IMAGE}${DOCKER_SNAPSHOT_SUFFIX}
        --build-arg BASE_TAG=${DOCKER_BUILD_TAG}