Using generated Kotlin from JPMS

[sgammon]

I've run into an issue with generated Pkl code in Kotlin. There does not appear to be an option in the Gradle plugin to set a package path; as a result, generated Kotlin ends up in the root package, which can't be exported from a Java module.

This could be fixed by adding an input argument to the code generator which sets a package path, to be included as package ... at the top of the generated code files.