[CI/CD] use predefined CI user creds

.gitlab-ci.yml

@@ -48,7 +48,7 @@ build_client:
   services:
     - docker:19.03.12-dind
   before_script: 
-    - docker login -u $GPT_REGISTRY_USER -p $GDT_REGISTRY_PASSWORD $CI_REGISTRY
+    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
   variables: 
     CLIENT_IMAGE_TAG: registry.beuth-hochschule.de/devops-project/app/client:$CI_COMMIT_TAG
     CLIENT_RELEASE_IMAGE_TAG: registry.beuth-hochschule.de/devops-project/app/client:latest
@@ -70,7 +70,7 @@ build_server:
   services:
     - docker:19.03.12-dind
   before_script: 
-    - docker login -u $GPT_REGISTRY_USER -p $GDT_REGISTRY_PASSWORD $CI_REGISTRY
+    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
   variables: 
     SERVER_IMAGE_TAG: registry.beuth-hochschule.de/devops-project/app/server:$CI_COMMIT_TAG
     SERVER_RELEASE_IMAGE_TAG: registry.beuth-hochschule.de/devops-project/app/server:latest
@@ -90,7 +90,7 @@ build_server:
 #   services:
 #     - docker:19.03.12-dind
 #   before_script: 
-#     - docker login -u $GPT_REGISTRY_USER -p $GDT_REGISTRY_PASSWORD $CI_REGISTRY
+#     - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
 #   script:
 #     - docker image ls -a
 #     - docker image prune