lua: add constructor and file ops for WpConf

This exposes the ability to load a SPA-JSON representation of a WpConf
object from an arbitrary file on disk to the Lua API

Signed-off-by: James Calligeros <jcalligeros99@gmail.com>

modules/module-lua-scripting/api/api.lua

@@ -184,6 +184,9 @@ local Feature = {
   },
 }
 
+-- Allow calling Conf() to instantiate a new WpConf
+WpConf["__new"] = WpConf_new
+
 SANDBOX_EXPORT = {
   Debug = Debug,
   Id = Id,