Prism proxy does not support GET/HEAD requests with bodies

[daniel-white]

Per the HTTP specifications, request bodies are discouraged for GET, HEAD and DELETE. Internally, Prism does not support this in proxy mode due to using the node-fetch package which conforms to the fetch standard. Prism will return PROXY_UNSUPPORTED_REQUEST_BODY when this is detected and not call the upstream server. Prism assumes are request body exists if either the Content-Length or Transfer-Encoding headers are specified.

If you desire this behavior and have a willingness for a pull request, packages/http/src/forwarder/index.ts would need to use another HTTP client, perhaps Node's http/https directly.