(#23116) Provide pluggable SSL verification

This provides the ability to create a verifier for SSL connections opened
with puppet's Puppet::Network::HTTP::Connection. The verifier is provided
the Net::HTTP connection and it just needs to configure it for the correct
verification mode.

The new functionality can be used when puppet's standard SSL verification
rules are not suited to the needs of the caller. The impetus for this was
a requirement that a connection be able to be made, the certificates
checked, but the subject and alt name checks skipped. Rather than put that
directly into puppet, this allows a new validator to be written that
performs those checks.