Support adding to karma files

[goncalossilva]

It'd be great if there was support for adding additional karma files.

Something like:

karma {
  files = [pattern: "resources/main/tzdata-latest/**", watched: false, served: true, included: false]
}

This could be achieved by concatenating here:

kotlin-frontend-plugin/kotlin-frontend/src/main/kotlin/org/jetbrains/kotlin/gradle/frontend/karma/KarmaConfigTask.kt

Lines 36 to 38 in b7f82d8

	"files" to listOf<String>(
	kotlinTestOutput(project).absolutePath
	),

This would enable workflows where the code being tested needs access to external resources.