Proxy drops Content-Type and other headers

[Nuru]

When a client makes a PUT request to the proxy, many headers are dropped or changed.

I have confirmed that Content-Type, Content-Length, Accept: */*, are dropped and Transfer-Encoding: chunked is added.

User-Agent is replaced with Go-http-client/1.1

These are varying degrees of bad, but the deal-killer for me is that by dropping Content-Type it breaks Elasticsearch, which requires a Content-Type header as of version 6.0