Introduce a KGraphQL Kotlin Compiler Plugin

[jeggy]

I don't have any compiler plugin experience, but I guess it would be possible to create a plugin that would validate the schema at compile time instead of runtime, making development safer.

Example in #71 we define a interface, and then when implementing that interface in a new type, we would get an error right within IntelliJ that we need to implemented the defined properties from the interface.