Issue #3673: build the release images on Github

and push the built Docker images to Docker Hub.
The activation was done be changing the watched tags to the release tags.

.github/workflows/docker_image_builder_rel.yml

@@ -15,7 +15,7 @@ on:
   # But usually the release tagging is done in an automated process.
   push:
     tags:
-      - test-[0-9]+_[0-9]+_[0-9]+_*
+      - rel-[0-9]+_[0-9]+_[0-9]+_*
 
 jobs:
   BuildDockerImage: