Creates test request helper for API endpoints

Separates common utils into the medusa-core-utils package.
Sets up a testing environment where mocked models/services/etc. can be placed in
__mocks__ folder within its corresponding directory. The mocks will
automatically be registered in a awilix container only used for testing.

packages/medusa-core-utils/.babelrc

@@ -0,0 +1,9 @@
+{
+  "plugins": ["@babel/plugin-proposal-class-properties"],
+  "presets": ["@babel/preset-env"],
+  "env": {
+    "test": {
+      "plugins": ["@babel/plugin-transform-runtime"]
+    }
+  }
+}