Add ProxyConectionFactory for enabling the proxy protocol.

[tyagiakhilesh]

Problem:

A DW service running behind a proxy/LB need to know the real source of the request. Attempt to solve #1176

Solution:

Proxy-Protocol is one the solution for this. Jetty has inbuilt support for it. We just need to utilize that.

Result:

request.getRemoteAddr() and request.getRemoteHost() shall give you information about the client that is making the request to proxy not of proxy itself (which is the case as of today without this feature).

[tyagiakhilesh]

Tests are failing of course, as by default the proxy protocol must be disabled. Once I figure out a way to make it configurable, things shall start looking better.

[jplock]

@tyagiakhilesh thanks for this, is there anyway to provide a test that it gets enabled when useProxyProtocol is set to true?

[tyagiakhilesh]

@jplock Done. Added the test case. Note: it is deliberate that I am finding the specific object at index 0 (in the last commit - in test case). Otherwise feature does not work.

[jplock]

Thanks @tyagiakhilesh, sorry I should have mentioned this before as well, but would you mind adding an entry under the 2.0.0 release notes in https://github.com/dropwizard/dropwizard/blob/master/docs/source/about/release-notes.rst for this PR? Then this should be good to merge.

[jplock]

LGTM once the release notes are updated

[tyagiakhilesh]

@jplock Updated release notes.