refactor: 💡 add standalone server mocks to auth tests (#1283)

* refactor: 💡 replace ember notify with flash in notify decorator

* refactor: 💡 remove embery-notify and replace last instance

* chore: 🤖 upgrade ember dependencies in anticipation of ember 4

* refactor: 💡 add standalone server mocks to auth tests

Co-authored-by: Susmitha Girumala <susmitha@hashicorp.com>

addons/auth/package.json

@@ -35,7 +35,6 @@
     "@glimmer/component": "^1.1.2",
     "@glimmer/tracking": "^1.1.2",
     "broccoli-asset-rev": "^3.0.0",
-    "core": "*",
     "doctoc": "^2.2.0",
     "ember-cli": "^4.4.0",
     "ember-cli-dependency-checker": "^3.2.0",
@@ -59,6 +58,7 @@
     "eslint-plugin-qunit": "^7.3.0",
     "loader.js": "^4.7.0",
     "npm-run-all": "^4.1.5",
+    "pretender": "^3.4.3",
     "prettier": "^2.4.0",
     "qunit": "^2.17.1",
     "qunit-dom": "^2.0.0",