Allow PUT method to hosts behind the misc Varnish cluster

RESTful applications often use a wider variety of HTTP methods than the
MediaWiki stack has traditionally required. This change provides
a mechanism for individual Varnish clusters to describe the set of
methods that they will allow via a regular expression. The default
behavior is to preserve the historical list of GET, HEAD, POST and
PURGE.

The PUT method is being added to misc at this time specifically to
support the dashboard save feature of the Kibana frontend used for
logstash.wikimedia.org.

Bug: 60350
Change-Id: Iea96bbedd8f351e3452f0dc2aaf3a9d42d78b165