licensing-summary-availability: Add test case

Add a new test case to confirm that a licensing summary is generated for minimal
and target images.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>

test-cases/licensing-summary-availability.yaml

+metadata:
+  name: licensing-summary-availability
+  format: "Apertis Test Definition 1.0"
+  image-types:
+    minimal: [ armhf-internal, armhf, arm64, amd64 ]
+    target:  [ armhf-internal, armhf, arm64, amd64 ]
+  image-deployment:
+    - APT
+    - OSTree
+  type: functional
+  exec-type: manual
+  priority: high
+  maintainer: "Apertis Project"
+  description: "Test the availability of the licensing summary."
+
+  expected:
+    - "A file <image_name>.img.licenses.gz should be present showing the licensing information."
+    - "The file should have the following json format:"
+    -
+      "{'image_licenses': [], 'packages': []}"
+
+    - "As an example:"
+    -
+      "{'image_licenses': ['LGPL-2+', 'BSD-3-clause or LGPL-2+', 'LGPL-2', 'BSD-2-clause'], 'packages': []}"
+
+run:
+  steps:
+    - "Navigate to the download folders where the image is published."
+    - "Ensure there's a <image_name>.img.licenses.gz file matching each image."
+    - "Download the <image_name>.img.licenses.gz file, decompress and open it in a text editor"