Allow Body greater than 1MB

Currently sumo_rest assumes the body of the request to be around 1MB, or crash otherwise.

https://github.com/inaka/sumo_rest/blob/7e1a494cf63c4732bde7f4dcee6b198f8441e144/src/sr_request.erl#L31
https://ninenines.eu/docs/en/cowboy/1.0/manual/cowboy_req/index.html#request_body_related_exports