Add Registrant API contact update action

Closes #849

test/models/action_test.rb

@@ -0,0 +1,20 @@
+require 'test_helper'
+
+class ActionTest < ActiveSupport::TestCase
+  setup do
+    @action = actions(:contact_update)
+  end
+
+  def test_fixture_is_valid
+    assert @action.valid?
+  end
+
+  def test_invalid_with_unsupported_operation
+    @action.operation = 'invalid'
+    assert @action.invalid?
+  end
+
+  def test_notification_key_for_contact
+    assert_equal :contact_update, @action.notification_key
+  end
+end