DEV: Convert tl4_delete_posts_and_topics to groups (#24866)

We're changing the implementation of trust levels to use groups. Part of this is to have site settings that reference trust levels use groups instead. It converts the tl4_delete_posts_and_topics  site setting to delete_all_posts_and_topics_allowed_groups.

This one is a bit different from previous ones, as it's a boolean flag, and the default should be no group. Pay special attention to the migration during review.

db/migrate/20231213103248_fill_delete_all_posts_and_topics_allowed_groups_based_on_deprecated_settings.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+class FillDeleteAllPostsAndTopicsAllowedGroupsBasedOnDeprecatedSettings < ActiveRecord::Migration[
+  7.0
+]
+  def up
+    currently_enabled =
+      DB.query_single(
+        "SELECT value FROM site_settings WHERE name = 'tl4_delete_posts_and_topics' AND value = 't' LIMIT 1",
+      ).first
+
+    if currently_enabled == "t"
+      # Matches Group::AUTO_GROUPS to the trust levels.
+      tl4 = "14"
+
+      # Data_type 20 is group_list.
+      DB.exec(
+        "INSERT INTO site_settings(name, value, data_type, created_at, updated_at)
+        VALUES('delete_all_posts_and_topics_allowed_groups', :setting, '20', NOW(), NOW())",
+        setting: tl4,
+      )
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigrationError
+  end
+end