Add admin API for managing canonical e-mail blocks (#19067)

config/routes.rb

@@ -602,6 +602,12 @@ Rails.application.routes.draw do
         post :measures, to: 'measures#create'
         post :dimensions, to: 'dimensions#create'
         post :retention, to: 'retention#create'
+
+        resources :canonical_email_blocks, only: [:index, :create, :show, :destroy] do
+          collection do
+            post :test
+          end
+        end
       end
     end