Disable puppet-agent when on buster

Unfortunately there aren't puppetlabs packages for buster yet, and
they'll probably take a while to actually arrive, but Debian has pretty
updated puppet packages at least (and finally has Facter 3.x!)

hiera.yaml

@@ -18,10 +18,10 @@ hierarchy:
     path: "type/%{::type}.yaml"
 
   - name: "Virtual or physical"
-    path: "is_virtual/%{::is_virtual}"
+    path: "is_virtual/%{::is_virtual}.yaml"
 
   - name: "OS version"
-    path: "os/%{::lsbdistcodename}"
+    path: "os/%{::lsbdistcodename}.yaml"
 
   - name: "Common defaults"
     path: "common.yaml"

hieradata/os/buster.yaml

@@ -0,0 +1,2 @@
+# TODO: Remove this once puppetlabs releases packages for buster
+puppet_agent: false