Add option to set canonical_url to embed_url

Hey @simon, I was struggling to find for a solution to set canonical URLs on selected topics in my community when I ran into this post.

It seems that this setting might offer a solution but I don’t understand what are “embedded topics”. I’ve tried looking for it on this community but I couldn’t find any explainers. Maybe this is something very basic. But will you be able to tell me what are embedded topics or how to embed topics in a Discourse community?