Add simple admin overview of PuSH subscriptions

app/controllers/admin/pubsubhubbub_controller.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class Admin::PubsubhubbubController < ApplicationController
+  before_action :require_admin!
+
+  layout 'public'
+
+  def index
+    @subscriptions = Subscription.includes(:account).paginate(page: params[:page], per_page: 40)
+  end
+end