Add the license scanning step to the pipeline

Run license scans for merge requests. If no files with UNKNOWN license found, commit the newly generated file and push it to the source branch so that it gets included in the merge request.

For licenses blacklisted in target, LICENSE_BLACKLIST can be set to a colon-separated list in the CI/CD settings of @pkg/target.

This doesn’t allow updating merge requests when the source branch is not in the same repository.