gilab-ci: Apply all `latest` tags once everything else succeeded

By applying `latest` tags as soon as the relevant image has been built
we end up with a quite large time window where they are all quite out
of sync: in particular, the tag is applied to the `base` image as soon
as it is ready, before all the depending images get built.

On top of that, if depending images fail, the `latest` tags will stay
out of sync.

This can be quite confusing for users, so let's apply the `latest` tag
only after all the previous stages have completed.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

.gitlab-ci.yml

@@ -178,56 +178,41 @@ test-flatdeb-builder:
 publish-base-docker-image:
   extends: .publish-docker-image
   stage: publish images
-  needs:
-     - build-base-docker-image
   variables:
     image: base
 
 publish-package-builder-docker-image:
   extends: .publish-docker-image
   stage: publish images
-  needs:
-     - build-package-builder-docker-image
   variables:
     image: package-builder
 
 publish-package-source-builder-docker-image:
   extends: .publish-docker-image
   stage: publish images
-  needs:
-     - build-package-source-builder-docker-image
   variables:
     image: package-source-builder
 
 publish-documentation-builder-docker-image:
   extends: .publish-docker-image
   stage: publish images
-  needs:
-     - build-documentation-builder-docker-image
   variables:
     image: documentation-builder
 
 publish-testcases-builder-docker-image:
   extends: .publish-docker-image
   stage: publish images
-  needs:
-     - build-testcases-builder-docker-image
   variables:
     image: testcases-builder
 
 publish-image-builder-docker-image:
   extends: .publish-docker-image
   stage: publish images
-  needs:
-     - test-image-builder-shared-runner
-     - test-image-builder-kvm-runner
   variables:
     image: image-builder
 
 publish-flatdeb-builder-docker-image:
   extends: .publish-docker-image
   stage: publish images
-  needs:
-     - test-flatdeb-builder
   variables:
     image: flatdeb-builder