Add Kotlin publishing and testing examples

[0xnm]

Another addition for #3451: it adds publishing and testing examples for Kotlin.

The only thing that needs to be mentioned is test filtering in Kotest: it doesn't have package.class.method format to do the filtering, instead it is using specs + classes parameters (see here).

Also mockito-kotlin requires JVM bytecode target to be 11.

[lihaoyi]

Thanks @0xnm, looks great. I'll close out the bounty and possibly open up some further ones for the next steps in the kotlin support effort