Provide GitHub action

[eirikb]

Discussed in #75

^{Originally posted by koppor May 17, 2025}
When using gradle on GitHub, it is advisable to use the setup-gradle action, because it optimizes caching

When I switch from gradlew to gg and if I want to have some caching, I have to use setup-gradle and I have to maintain the gradle version both in the call of gg (or the gradle.properties entry), and in gradle-version of setup-gradle action.

With a gg-action, would not be required to use setup-gradle any more and could just use gg.