Documentation: Add some examples with the Kotlin DSL

[juherr]

Currently, all samples from https://github.com/autostyle/autostyle/tree/master/plugin-gradle are using the Groovy DSL.
Adding some examples with the Kotlin DSL could help Gradle newbies like me to save time.

For example:

configure<AutostyleExtension> {
    val ktlintVersion = "0.41.0"
    kotlin {
        ktlint(ktlintVersion)
        trimTrailingWhitespace()
        endWithNewline()
    }
    kotlinGradle {
        ktlint(ktlintVersion)
        trimTrailingWhitespace()
        endWithNewline()
    }
}