Add wrapper-upgrade-gradle-plugin

[StefMa]

Right now this project uses Gradle 8.1 (released April 12th).

When using the https://github.com/gradle/wrapper-upgrade-gradle-plugin we will get automatically a PR as soon as new Gradle release happen (periodically).

[sschuberth]

I guess more generally https://github.com/renovatebot/renovate or https://github.com/dependabot/dependabot-core could be used to keep any dependency up-to-date.

[StefMa]

Gradle (wrapper) is not a dependency, but the build tool itself 🤓
AFAIK, dependabot can't handle this.
Seems renovate is capapable to do so.

[sschuberth]

Well, of course your build depends on a build tool 😉 And yes, we're using Renovate successfully to update the Gradle wrapper.