(#9546) Add external fact pluginsync

Add pluginsync to <module>/facts.d directory and load these as external facts during the client run.  This PR is dependent on https://github.com/puppetlabs/facter/commit/6f19eeeef1c5c8e9cc84c44599e03a5c06a30abc which will be in facter 2.0.  Puppet.feature.external_facts? was added to prevent errors when facts < 2.0.