uploads: add upload_media_assets.page_url.

This is needed for multi-file uploads. We need to know both the image
url and the page url to set the post's source correctly when converting
an upload media asset into a post.

app/models/upload_media_asset.rb

@@ -12,7 +12,7 @@ class UploadMediaAsset < ApplicationRecord
   }
 
   def self.search(params)
-    q = search_attributes(params, :id, :created_at, :updated_at, :status, :source_url, :error, :upload, :media_asset)
+    q = search_attributes(params, :id, :created_at, :updated_at, :status, :source_url, :page_url, :error, :upload, :media_asset)
     q.apply_default_order(params)
   end
 end