Add administrative webhooks (#18510)

* Add administrative webhooks

* Fix error when webhook is deleted before delivery worker runs

spec/models/webhook_spec.rb

@@ -0,0 +1,32 @@
+require 'rails_helper'
+
+RSpec.describe Webhook, type: :model do
+  let(:webhook) { Fabricate(:webhook) }
+
+  describe '#rotate_secret!' do
+    it 'changes the secret' do
+      previous_value = webhook.secret
+      webhook.rotate_secret!
+      expect(webhook.secret).to_not be_blank
+      expect(webhook.secret).to_not eq previous_value
+    end
+  end
+
+  describe '#enable!' do
+    before do
+      webhook.disable!
+    end
+
+    it 'enables the webhook' do
+      webhook.enable!
+      expect(webhook.enabled?).to be true
+    end
+  end
+
+  describe '#disable!' do
+    it 'disables the webhook' do
+      webhook.disable!
+      expect(webhook.enabled?).to be false
+    end
+  end
+end