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)
   Γ— returns the authentication token on successful authentication
This confirms that MSW can intercept the request made in getAuthToken(). But the test itself is still failing!
Caused by: Error: getaddrinfo ENOTFOUND api.example.com
Although the error is caused by requesting a non-existent URL, the real issue is that we're still allowing the test to make the actual request.
That's right, MSW operates in pass-through mode by default, allowing all intercepted requests to proceed unless instructed otherwise.
It is time for us to change that by mocking the request with MSW!