reponse headers are ignored.

[gjselten]

When using this graphql client, i am unable to get the response headers. Only the response body is parsed and returned:

https://github.com/github/graphql-client/blob/a0f782c6edccdebdaaf31020b4597331675239ad/lib/graphql/client/http.rb#L76

This is inconvenient as headers might contain useful information.

[tjoyal]

I've been struggling myself with this issue and I think we should fine a path to fix it.

Linking items, https://github.com/github/graphql-client/pull/249 has an attempt for it.