Add highlighting for Kotlin

[daincredibleholg]

Is your feature request related to a problem? Please describe

I am one of the Java Advent organizers and with Kotlin's popularity going further through the roof it starts getting problematic that articles about Kotlin can't have properly highlighted code snippets.

Describe the solution you'd like

In addition to [java], a [kotlin] block (and similar) would be helpful

[krzema12]

Hi @daincredibleholg, in my 2022 article for Java Advent I used embedded GitHub Gists snippets, see https://www.google.com/amp/s/www.javaadvent.com/2022/12/how-i-got-rid-of-yaml-in-githubs-ci.html/amp. The only disadvantage I see is that the article isn't self-contained, so if someone removes the gist, the article will lose the piece of code as well. Anyway, I think it's a good workaround at least.

[daincredibleholg]

You are absolutely correct, @krzema12. For now, it should do. We need a more portable / independent fix, though.