Support Proxy protocol with HAProxy in Bitbucket DC

Problem Definition

If you're using Bitbucket Data Center with SSH load balancing over tcp backend on Bitbucket node the access logging is useless because all the IPs are overwritten to the IP address of load balancer itself.

Suggested Solution

Provide support for Proxy protocol supported by HAProxy: http://www.haproxy.org/download/1.8/doc/proxy-protocol.txt

Why this is important

It will allow to use Bitbucket audit and access logging functionality while using load balancing from HAProxy.