fix(ci): export IMAGE_TAG variable for better clarity in build process

.gitlab-ci.yml

@@ -29,10 +29,11 @@ workflow:
     - echo "DEBUG----- $(date '+%Y-%m-%d %H:%M:%S') Starting build process"
     - |
       if [ -n "$CI_COMMIT_TAG" ]; then
-        echo "IMAGE_TAG=${CI_COMMIT_TAG#sub2api/}"
+        export IMAGE_TAG="${CI_COMMIT_TAG#sub2api/}"
       else
-        echo "IMAGE_TAG=$CI_COMMIT_REF_NAME"
+        export IMAGE_TAG="$CI_COMMIT_REF_NAME"
       fi
+      echo "Image tag: $IMAGE_TAG"
     - echo "Logging into Harbor..."
     - echo "$HARBOR_PASSWORD" | docker login -u "$HARBOR_USERNAME" --password-stdin "$HARBOR_SERVICE"
     - docker build -f Dockerfile --build-arg VERSION="${VERSION}" --build-arg COMMIT="${COMMIT}" --build-arg DATE="${DATE}" -t "$HARBOR_SERVICE/$HARBOR_REGISTRY/sub2api:${IMAGE_TAG}" .