My Jenkins warnings and coverage plugins can be used directly in GitHub or GitLab pipelines now. I extracted the models and parser for both plugins into separate models, so you can use them in libraries or other applications. In GitHub pipelines you can use the Quality Monitor GitHub Action to visualize warnings and code coverage. The same action is available as Autograding Action for GitLab.
Since there is no Jenkins server or UI available in such pipelines the output is somewhat limited:
You also will get some details about the warnings and the coverage as PR comment and as source code annotations. Additionally, you can create badges for all available metrics.