Implement a debdiff workflow and integrate it in the debian_pipeline one

In %STF M4: workflow for security team we created a debdiff task but we have to make it easier to use in a workflow with the help of a debdiff workflow. And then we need to make it easy to enable that workflow as a sub-workflow of debian_pipeline.

I expect the debdiff workflow to need:

• source_artifact
• binary_artifacts
• the debian:suite that will be used to find the corresponding artifacts used as comparison point