Change notifications API to use a replica (#25874)

app/helpers/database_helper.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module DatabaseHelper
+  def with_read_replica(&block)
+    ApplicationRecord.connected_to(role: :read, prevent_writes: true, &block)
+  end
+
+  def with_primary(&block)
+    ApplicationRecord.connected_to(role: :primary, &block)
+  end
+end