Toggle PROXY protocol support on/off

[minorOffense]

Add an option for varnish to recognize the PROXY protocol. Allows a setup similar to https://feryn.eu/blog/varnish-4-1-haproxy-get-the-real-ip-by-leveraging-proxy-protocol-support/

This adds a boolean option which will add the ',PROXY' string to the end of the port definition.

[NITEMAN]

@minorOffense PROXY protocol is already supported, we have been using something like this on hiera for ages:

varnish::listen:
  - '0.0.0.0:6081'
  - '0.0.0.0:6083,PROXY'

IMHO adding that option makes the module less flexible

[minorOffense]

It doesn't work if you use listen addr and port separately. You end up having to build the config string by hand (like in your example). The boolean just makes it more convenient and works with the other options independently.

[NITEMAN]

Maybe I'm wrong, but if the new parameter is set to true it applies to every item on varnish::listen... I think at least parameter documentation should state it clearly (something like "Boolean toggle for conveniently appending ,PROXY to all items on $listen" instead of "Boolean toggle support for the PROXY protocol.")