Document code style

[aSemy]

The PR template says to use the code style

https://github.com/JetBrains/gradle-intellij-plugin/blob/0e1bd547c1aede452ffb6e7af0cf53ea080038e2/.github/pull_request_template.md?plain=1#L41

However I'm not clear about which code style to use. I've tried using the Kotlin default style, but this caused a lot of changes.

Please can you either commit the code style into the .idea directory, or export the style to a .editorconfig file? Thanks!

I think it would also help to add guidance to CONTRIBUTING.md