Added push to gitlab registry

.gitlab-ci.yml

+image: docker:20
 services:
-  - docker:dind
+  - docker:20-dind
 
 stages:
   - build
+  - release
   - deploy
 
+variables:
+  CONTAINER_TEST_IMAGE: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG
+  CONTAINER_RELEASE_IMAGE: $CI_REGISTRY_IMAGE:latest
+  CONTAINER_QA_IMAGE: $CI_REGISTRY_IMAGE:nightly
+
+before_script:
+  - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
+
 build:
   stage: build
-  variables:
-    IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG
   script:
-    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
-    - docker build -t $IMAGE_TAG .
-    - docker push $IMAGE_TAG
+    - docker build -t $CONTAINER_TEST_IMAGE .
+    - docker push $CONTAINER_TEST_IMAGE
+  only:
+    - main
+    - develop
+    - /^release-.*$/
+
+release_prod:
+  stage: release
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker tag $CONTAINER_TEST_IMAGE $CONTAINER_RELEASE_IMAGE
+    - docker push $CONTAINER_RELEASE_IMAGE
   only:
     - main
+
+release_qa:
+  stage: release
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker tag $CONTAINER_TEST_IMAGE $CONTAINER_RELEASE_IMAGE
+    - docker push $CONTAINER_QA_IMAGE
+  only:
     - develop
-    - /^release-.*$/
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