feat: use official singularity image

This would remove the need to maintain a special dind image.

.gitlab-ci.yml

 image: eicweb.phy.anl.gov:4567/containers/image_recipes/ubuntu_dind:latest
 
 variables:
+  ## External images
+  DOCKER_IMAGE: docker.io/docker:24.0.5
+  SINGULARITY_IMAGE: quay.io/singularity/singularity:v3.11.4
+
   ## Application versions used for the main release 
   ## note: nightly builds will always use the master/main branch
   JUGGLER_VERSION: "v10.0.1"
@@ -407,6 +411,7 @@ jug_xl:nightly:
                    containers/jug
 
 .singularity:
+  image: ${SINGULARITY_IMAGE}
   stage: deploy
   interruptible: true
   rules: