Add webhook templating (#23289)

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

db/migrate/20230129023109_add_template_to_webhooks.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddTemplateToWebhooks < ActiveRecord::Migration[6.1]
+  def change
+    add_column :webhooks, :template, :text
+  end
+end