extlib__puppet_config: Add environment settings

```json
{
  "extlib__puppet_config": {
    "master": {
      "localcacert": "/etc/puppetlabs/puppet/ssl/certs/ca.pem",
      "ssldir": "/etc/puppetlabs/puppet/ssl"
    },
    "main": {
      "hostpubkey": "/etc/puppetlabs/puppet/ssl/public_keys/puppet.local.pem",
      "hostprivkey": "/etc/puppetlabs/puppet/ssl/private_keys/puppet.local.pem",
      "hostcert": "/etc/puppetlabs/puppet/ssl/certs/puppet.local.pem",
      "localcacert": "/etc/puppetlabs/puppet/ssl/certs/ca.pem",
      "ssldir": "/etc/puppetlabs/puppet/ssl",
      "vardir": "/opt/puppetlabs/puppet/cache",
      "server": "puppet.local",
      "environment": "production"
    },
    "agent": {
      "environment": "production"
    }
  }
}
```

lib/facter/extlib__puppet_config.rb

@@ -17,7 +17,9 @@
         ssldir
         vardir
         server
-      ]
+        environment
+      ],
+      agent: %i[environment],
     }
 
     desired_settings.each_pair do |section, settings|