Investigate content negotiation

[lkitching]

Investigate whether content types other than JSON (e.g. EDN, CSV) can be negotiated.

[RickMoynihan]

FYI: I've asked the lacinia authors on the #graphql clojure slack channel about this, waiting to hear back... but the lacinia-pedestal docs say "The response format is always application/json."

[RickMoynihan]

Looks like there are plans also to support graphql like queries via an EDN serialisation of the query: https://github.com/walmartlabs/lacinia-pedestal/issues/12#issuecomment-307196248 This would be awesome for any clients we write, but note also they seem up for negotiating transit and other response types.