DEV: Adds new plugin API support to always show the topic map (#12642)

You can enable this by using the `includePostAttributes` API call with
the value of `topicMap`. This will always show the topic map at the top
of a topic regardless of how many posts there are.

app/assets/javascripts/discourse/app/lib/transform-post.js

@@ -172,6 +172,7 @@ export default function transformPost(
   }
 
   const showTopicMap =
+    _additionalAttributes.indexOf("topicMap") !== -1 ||
     showPMMap ||
     (post.post_number === 1 &&
       topic.archetype === "regular" &&