Improve documentation on the use of Object Mapper in driver 4.x with Kotlin

Provide full example of configuring Maven to compile Kotlin code + generated files. For example, Maven compile plugin need to be after the kapt, etc. See this SO answer & links for more details: https://stackoverflow.com/questions/62694080/codec-not-found-for-requested-operation-mapvarchar-int-java-util-map/62696422#62696422

It also would be useful to provide Kotlin examples as part of repo