[KOTLIN] [SPRING] Fixes for: invoker-package / Jackson Module / Configuration / Misc

Created by: dr4ke616

There are a number of minor bugs that this issue will look to highlight within the Kotlin Code Generator. Ideally these all should be small enough to be fixed as part of a single PR.

Description

• Set the basePackage from invokerPackage so can be picked up from the --invoker-package argument.
• Add the Kotlin Jackson module to support serialization/deserialization of Kotlin classes and data classes
• The base path configuration property key in the RequestMapping annotation of each controller is generated from openapi.{{title}}.base-path. It might be better to clean this a little and just use something like api.base-path, as all child routes are injected as part of each methods RequestMapping.
• The application configuration doesn't work. It's generated as a .yaml file, but the format of the file is .properties. Update the template to use yaml structure. E.g change to something like below:

spring:
  application:
    name: someApiTitle

  jackson:
    serialization:
      WRITE_DATES_AS_TIMESTAMPS: false

server:
  port: 8080

openapi-generator version

• org.openapitools:openapi-generator:3.2.3