Use GitHub action to add new contributors to the list

[Feichtmeier]

Add authors of commit automatically to the authors file (if absent) via a github action

[Jupi007]

That's a really good idea!

[Feichtmeier]

HTTP GET https://api.github.com/repos/ubuntu-flutter-community/software/contributors

https://docs.github.com/de/rest/repos/repos?apiVersion=2022-11-28#list-repository-contributors

[d-loose]

app-center uses this package to fetch the list of contributors shown on the about page.