fixes gh-2860

* Handle GZip response from downstream with an empty body.

fixes gh-2807

* Always forward Content-Length from origin when set unless response is compressed and client does not support it

Fix for #2832

* Add test cases to assert behaviour with regards to the Content-Length header

Polishes tests.

fixes gh-2784

fixes gh-2782

see https://github.com/reactor/reactor-netty/issues/292