FEATURE: Silence Close Notifications User Setting (#26072)

This change creates a user setting that they can toggle if
they don't want to receive unread notifications when someone closes a
topic they have read and are watching/tracking it.

db/migrate/20240307231053_add_topics_unread_when_closed_to_user_options.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddTopicsUnreadWhenClosedToUserOptions < ActiveRecord::Migration[7.0]
+  def change
+    add_column :user_options, :topics_unread_when_closed, :boolean, default: true, null: false
+  end
+end