Investigate OAS/Swagger generation of client

[LordMike]

On the V4's documentation page, there are links to OAS / RAML specs for the API. We could generate a lot of code from these specifications, and then code the few differentiations there are for an actual client (overloads and whatnot) -- I imagine we'll also encounter cases where two responses/requests use the same object, but where the spec specifies different objects.

However, currently (was also the case last I tried swagger on this) the spec is incomplete or invalid: https://www.themoviedb.org/talk/58691a749251414e7500c442

[LordMike]

The current OAS specs seem incomplete. For Movie f.ex., there are non of the "append_to_response" methods available as properties, so if we generated it from that, we would be missing those.

I suppose we could post-add those specifically, using partials.