ci(azure-pipelines): create basic Docker@2 task for building test image

azure-pipelines.yaml

@@ -6,7 +6,7 @@ pool: 'Prod Private Agent Pool'
 
 jobs:
 - job: HelloWorld
-  container:
+  container: &ubuntu
     image: 'devfra.azurecr.io/de.fraport.trusted/ubuntu:22.04'
     endpoint: devfra
   steps:
@@ -15,4 +15,15 @@ jobs:
   - script: |
       echo Add other tasks to build, test, and deploy your project.
       echo See https://aka.ms/yaml
-    displayName: 'Run a multi-line script'
+    displayName: 'Run a multi-line script'
+- job: ContainerTest
+  container: *ubuntu
+  steps:
+    - task: Docker@2
+      displayName: Image build test
+      inputs:
+        command: buildAndPush
+        Dockerfile: docker/backend/Dockerfile
+        buildContext: .
+        tags: backend
+