feat: storage policy API and mirage changes (#2054)

* feat: 🎸 add storage policy API and mirage

addons/api/addon/models/policy.js

@@ -0,0 +1,8 @@
+/**
+ * Copyright (c) HashiCorp, Inc.
+ * SPDX-License-Identifier: MPL-2.0
+ */
+
+import GeneratedPolicyModel from '../generated/models/policy';
+
+export default class PolicyModel extends GeneratedPolicyModel {}