Support `application/dns-json+json` and/or `application/dns+json` as aliases for `application/dns-json`


Right now, a query for or returns 415 Unsupported Media Type, and only returns 200 OK with a JSON payload, but a non‑JSON Media Type.

application/dns-json is unsupported by most JSON utilities, whereas application/dns-json+json and application/dns+json are, as their Media Type suffix is +json and they’re therefore considered to be JSON Media Types.

I propose to add support for application/dns-json+json and/or application/dns+json as aliases for application/dns-json.