Remove authentication checks from POST/PATCH/DELETE requests

[wopian]

kitsu currently throws an error if POST/PATCH/DELETE requests are attempted without the Authorization header being set.

This poses an issue in 2 places:

• APIs using non-standard headers for their authentication system (e.g. X-Something)
• APIs that allow guest usage (e.g comments) where authentication is not needed to send POST requests.

In both cases, if an unauthenticated request is to an endpoint that requires authentication, the JSON:API API returns its own (403) error in the expected JSON:API error format.