Junit Extensions for Test Impact Analysis
github.com
github.com
However, take in mind that the report is stored inside the Git repository as a note (it is invisible - and how other tools like Gerrit work) to avoid an external service.
The tool could generate the report as a file, sure. But The problem is that you will need a service to retrieve that file and compare - and then it becomes a non generic solution.
Indeed, my question is what do you want to do with that file? It can generate it, but nobody will take benefit of it, right?