Description

It would make our HTTP API slightly more ergonomic to use via curl if it didn't error when the Content-Type header is omitted.

This seems to be acceptable according to the HTTP spec:

https://stackoverflow.com/questions/15860742/is-content-type-mandatory-in-http-post-request

I think using application/json as the default for most endpoints is OK, as that's usually what one is munging around on the CLI. If the user is sending binary they should be savvy enough to set the header (we could maybe log a warning if the error message doesn't already make it clear enough that Lighthouse attempted to parse JSON data).