puppet: Allow /etc/zulip to be a symlink.

This PR updates the puppet manifest to allow /etc/zulip to be a symlink. The current behaviour overwrites /etc/zulip if it is link to another directory, which is problematic with docker-zulip and 
in particular the `LINK_SETTINGS_TO_DATA` setting.

puppet/zulip/manifests/base.pp

@@ -119,6 +119,7 @@ class zulip::base {
     mode   => '0644',
     owner  => 'zulip',
     group  => 'zulip',
+    links  => 'follow',
   }
   file { ['/etc/zulip/zulip.conf', '/etc/zulip/settings.py']:
     ensure  => 'file',