* feat: add companion object to data classes if the implement the interface java.io.Serializable
* style: format template file
* style: adapt to project's original code style
* fix: add missing imports
* style: reverted mustache template to original styling
* test: generate additional samples for kotlin-springboot-reactive and kotlin-springboot
* docs: name full qualified classname of interface java.io.Serializable to prevent confusion with kotlinx.serialization