OpenAPI Documentation + Kotlin DSL

[Syer10]

This continues #248 using a custom DSL that will help us write the endpoint documentation.

I tested the DSL on the manga retrieve endpoint and it works perfectly. I did not add any of the updates endpoint documentation, that can be done at a later time.

Description of previous PR:
Added https://javalin.io/plugins/openapi to Tachidesk.
There are now two new paths available:

/api/openapi.json - OpenApi Document in JSON Representation
/api/swagger-ui - Swagger Frontend to view API Documentation and use the API

OpenApi isn't able to document WebSockets as of now.
I fully documented the UpdateController using the dsl API. Which provides flexibility in the placement of the documentation.