[ci] Skip external releases if associated OUT_REGISTRY value is empty.

Allows CI/CD environment variables to quickly disable any release job derived from the .release:external template

Template Usage: DRYRUN_RELEASE set to a value to echo docker and regctl commands in Makefile without running them (dry-run) SKIP_RELEASE set to a value to remove the job from the pipeline.

CI/CD Usage: NGC_SKIP_RELEASE set to disable external release to NGC. DOCKERHUB_SKIP_RELEASE set to disable external release to DH. NGC_DRYRUN_RELEASE set to dry-run external release to NGC. DOCKERHUB_DRYRUN_RELEASE set to dry-run external release to DH.

.common-ci.yml

@@ -191,16 +191,24 @@ test-packaging:
 
 # Define an external release step that pushes an image to an external repository.
 # This includes a devlopment image off master.
+# NOTE: job is skipped if OUT_REGISTRY is null or empty. Can be used to disable release(s) with CI/CD env.
 .release:external:
   extends:
     - .release
   rules:
+    - if: '$OUT_REGISTRY == null || $OUT_REGISTRY == "" || $SKIP_RELEASE'
+      when: never
+    - if: '$DRYRUN_RELEASE'
+      variables:
+        DOCKER: echo
+        REGCTL: echo
     - if: $CI_COMMIT_TAG
       variables:
         OUT_IMAGE_VERSION: "${CI_COMMIT_TAG}"
     - if: $CI_COMMIT_BRANCH == $RELEASE_DEVEL_BRANCH
       variables:
         OUT_IMAGE_VERSION: "${DEVEL_RELEASE_IMAGE_VERSION}"
+    - when: on_success
 
 # Define the release jobs
 release:staging-centos7:

.nvidia-ci.yml

@@ -231,6 +231,8 @@ scan-ubi8-arm64:
     OUT_REGISTRY_TOKEN: "${NGC_REGISTRY_TOKEN}"
     OUT_REGISTRY: "${NGC_REGISTRY}"
     OUT_IMAGE_NAME: "${NGC_REGISTRY_IMAGE}"
+    SKIP_RELEASE: "${NGC_SKIP_RELEASE}"
+    DRYRUN_RELEASE: "${NGC_DRYRUN_RELEASE}"
 
 .release:dockerhub:
   extends:
@@ -240,6 +242,8 @@ scan-ubi8-arm64:
     OUT_REGISTRY_TOKEN: "${REGISTRY_TOKEN}"
     OUT_REGISTRY: "${DOCKERHUB_REGISTRY}"
     OUT_IMAGE_NAME: "${REGISTRY_IMAGE}"
+    SKIP_RELEASE: "${DOCKERHUB_SKIP_RELEASE}"
+    DRYRUN_RELEASE: "${DOCKERHUB_DRYRUN_RELEASE}"
 
 release:staging-ubuntu18.04:
   extends: