Add jenkins job for Kotlin precommit.

There's a Gradle task for a Kotlin precommit (:examples:kotlin:preCommit) but as far as I can tell it is not run anywhere. We should add a Jenkins job for it.

https://github.com/apache/beam/blob/d9d3c93c69c04c132310fe70be0ac243757460f7/examples/kotlin/build.gradle#L124