Setup Java in Kotlin MPP Example

[nomisRev]

The example module currently doesn't setup the Java app.
Upon setting up the example module we ran into some issues setting up Java from a Kotlin MPP project.

It didn't correctly link the Main-Class in the Manifest when configuring from the regular Java Gradle DSL.
Neither Google, nor Kotlin Slack gave me an quick solution so I opted to move it out of the scope of PR #4.