Resource Controller: Allow overriding authorize_resource

In a host app, I want to use scopes as resource models for index actions.
Scopes can not be authorized through CanCanCan like actual models can.

This is a pretty remote use case, so I won't try baking that into the
already pretty complex resource handling system. However, it would be
convenient to be able to override the authorization logic from my host app.
This commit achieves that.

app/controllers/alchemy/admin/resources_controller.rb

@@ -13,9 +13,7 @@ class ResourcesController < Alchemy::Admin::BaseController
       before_action :load_resource,
         only: [:show, :edit, :update, :destroy]
 
-      before_action do
-        authorize!(action_name.to_sym, resource_instance_variable || resource_handler.model)
-      end
+      before_action :authorize_resource
 
       def index
         @query = resource_handler.model.ransack(params[:q])
@@ -112,6 +110,10 @@ def load_resource
         instance_variable_set("@#{resource_handler.resource_name}", resource_handler.model.find(params[:id]))
       end
 
+      def authorize_resource
+        authorize!(action_name.to_sym, resource_instance_variable || resource_handler.model)
+      end
+
       # Permits all parameters as default!
       #
       # THIS IS INSECURE! Although only signed in admin users can send requests anyway, but we should change this.