Configure simple --json

[znd4]

Checklist

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Enhancement request

I'd like to be able to configure http s.t., if I

http --json http://some.server.foo

it will send Accept as exactly application/json.

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Problem it solves

Some servers don't correctly implement the media-type spec, instead using something like get_header("Accept") == "application/json", and it'd be nice to not have to switch to adding Accept: application/json.

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Additional information, screenshots, or code examples

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