Bug 21267: Set X-FORWARDED-PROTO https if required

Bug 21267: Set X-FORWARDED-PROTO https if required

This patch makes the apache configuration for the reverse proxy
(required for Plack) so it sets the X-FORWARDED-PROTO header correctly
for Plack::Middleware::ReverseProxy to use it.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Ulrich Kleiber <ulrich.kleiber@bsz-bw.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Since we actually resolve 19799 now (Changing language on OPAC redirects
back to homepage), I will move that code to a new enh report.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>