rate limit all doorkeeper controllers

using the same limit as user sessions

app/controllers/doorkeeper_base_controller.rb

@@ -0,0 +1,3 @@
+class DoorkeeperBaseController < ActionController::Base # rubocop:disable Rails/ApplicationController
+  rate_limit to: 10, within: 3.minutes
+end

config/initializers/doorkeeper.rb

@@ -2,7 +2,7 @@
 
 Doorkeeper.configure do
   orm :active_record
-  base_controller "ActionController::Base"
+  base_controller "DoorkeeperBaseController"
 
   # Enabled grant flows
   grant_flows %w[client_credentials]