Upgrade Gradle Version

[silvanheller]

Is your feature request related to a problem? Please describe.
Gradle 6 is incompatible with Java 17, which means it is annoying to develop on IntelliJ when working on Java 17 projects alongside DRES

Describe the solution you'd like
I'd like the Gradle version to be bumped to 7

Describe alternatives you've considered
The alternative is having to change some IntelliJ configurations everytime I work on DRES, which is more effort than bumping the Gradle version.
An even better option would be moving to Java 11+ and bumping the plugins which are used.

[lucaro]

I just upgraded to the latest version of gradle (v7.3) on dev. So far, I didn't observe any issues with it, but I'd like to test this some more. If nothing comes up, this will go into the next release.
I don't currently see any benefit of increasing the java source compatibility to anything above 8, since there are currently no kotlin features that would benefit as far as I'm aware.