chore: 🤖 migrate to ember-copy addon because of deprecations

addons/api/addon/serializers/application.js

@@ -1,6 +1,6 @@
 import RESTSerializer from '@ember-data/serializer/rest';
 import { underscore } from '@ember/string';
-import { copy } from '@ember/object/internals';
+import { copy } from 'ember-copy';
 
 /**
  * Manages serialization/normalization of data to/from the API.

addons/api/package.json

@@ -38,6 +38,7 @@
     "ember-cli-sri": "^2.1.1",
     "ember-cli-template-lint": "^1.0.0-beta.3",
     "ember-cli-uglify": "^3.0.0",
+    "ember-copy": "^1.0.0",
     "ember-data": "^3.16.0",
     "ember-disable-prototype-extensions": "^1.1.3",
     "ember-export-application-global": "^2.0.1",