FEATURE: Category setting to allow unlimited first post edits by the owner of the topic (#12690)

This PR adds a new category setting which is a column in the `categories` table, `allow_unlimited_owner_edits_on_first_post`.

What this does is:

* Inside the `can_edit_post?` method of `PostGuardian`, if the current user editing a post is the owner of the post, it is the first post, and the topic's category has `allow_unlimited_owner_edits_on_first_post`, then we bypass the check for `LimitedEdit#edit_time_limit_expired?` on that post.
* Also, similar to wiki topics, in `PostActionNotifier#after_create_post_revision` we send a notification to all users watching a topic when the OP is edited in a topic with the category setting `allow_unlimited_owner_edits_on_first_post` enabled.

This is useful for forums where there is a Marketplace or similar category, where topics are created and then updated indefinitely by the OP rather than the OP making new topics or additional replies. In a way this acts similar to a wiki that only one person can edit.

app/controllers/categories_controller.rb

@@ -296,6 +296,7 @@ class CategoriesController < ApplicationController
         :email_in_allow_strangers,
         :mailinglist_mirror,
         :all_topics_wiki,
+        :allow_unlimited_owner_edits_on_first_post,
         :parent_category_id,
         :auto_close_hours,
         :auto_close_based_on_last_post,