DEV: Switch over category settings to new table - Part 3 (#20657)

In #20135 we prevented invalid inputs from being accepted in category setting form fields on the front-end. We didn't do anything on the back-end at that time, because we were still discussing which path we wanted to take. Eventually we decided we want to move this to a new CategorySetting model.

This PR moves the require_topic_approval and require_reply_approval from custom fields to the new CategorySetting model.

This PR is nearly identical to #20580, which migrated num_auto_bump_daily, but since these are slightly more sensitive, they are moved after the previous one is verified.

spec/requests/topics_controller_spec.rb

@@ -1599,7 +1599,7 @@ RSpec.describe TopicsController do
       end
 
       it "can not move to a category that requires topic approval" do
-        category.custom_fields[Category::REQUIRE_TOPIC_APPROVAL] = true
+        category.require_topic_approval = true
         category.save!
 
         put "/t/#{topic.id}.json", params: { category_id: category.id }