FIX: Follow the canonical URL when importing a remote topic. (#14489)

FinalDestination now supports the `follow_canonical` option, which will perform an initial GET request, parse the canonical link if present, and perform a HEAD request to it.

We use this mode during embeds to avoid treating URLs with different query parameters as different topics.

app/models/topic_embed.rb

@@ -113,7 +113,8 @@ class TopicEmbed < ActiveRecord::Base
     fd = FinalDestination.new(
       url,
       validate_uri: true,
-      max_redirects: 5
+      max_redirects: 5,
+      follow_canonical: true,
     )
 
     url = fd.resolve