How to make new DiscourseEvent?

Hello, Everyone and Happy new year!

I want to create new discourse plugin which sends posts and replies to GitHub issues.
So, I fonund :post_created symbols on discourse-official-slack-plugin and used it (like below example code).

DiscourseEvent.on(:post_created) do |post_id|
   post_id = post_id[:id]

But I failed to find event when updated posts and replies. I think post_created symbol defined by PostAlterer class at app/services/post_alterer.rb.

Therefore, I want to know

  1. How to create events when update post or reply or where event defined.
  2. If it is impossible, May I modify controller code directly for implementing my features?

Taehwan Kim.