Set up MSW

With MSW set up, we can now run npm test and see the outgoing request's method and URL printed during the test run:
$ npm test

> test
> vitest

stdout | get-auth-token.test.ts > returns the authentication token on successful authentication
POST https://api.example.com/auth

 ❯ get-auth-token.test.ts (1)
   × returns the authentication token on successful authentication
This confirms that MSW is able to intercept the request we make in getAuthToken(). But the test itself is still failing!
Caused by: Error: getaddrinfo ENOTFOUND api.example.com
Althought the error is caused by us requesting a non-existing URL, the underlying issue is that we still allow the test to make the actual request.
That's right, MSW is transparent by default, and will allow all the intercepted requests to pass through unless you instruct it otherwise.
It is time for us to change that by mocking that request with MSW!