title: Gitlab CI: Set dynamic variables
body: <p>For a gitlab CI I'm defining some variables like this:</p>
  
  <pre><code>variables:
    PROD: project_package
    STAGE: project_package_stage
    PACKAGE_PATH: /opt/project/build/package
    BUILD_PATH: /opt/project/build/package/bundle
    CONTAINER_IMAGE: registry.example.com/project/package:e2e
  </code></pre>
  
  <p>I would like to set those variables a bit more dynamically, as there are mainly only two parts: <code>project</code> and <code>package</code>. Everything else depends on those values, that means I have to change only two values to get all other variables.</p>
  
  <p>So I would expect something like</p>
  
  <pre><code>variables:
    PROJECT: project
    PACKAGE: package
    PROD: $PROJECT_$PACKAGE
    STAGE: $PROD_stage
    PACKAGE_PATH: /opt/$PROJECT/build/$PACKAGE
    BUILD_PATH: /opt/$PROJECT/build/$PACKAGE/bundle
    CONTAINER_IMAGE: registry.example.com/$PROJECT/$PACKAGE:e2e
  </code></pre>
  
  <p>But it looks like, that the way doing this is wrong...</p>