Feedback: rename configuration properties

The `Configuration` object should take a `clientId` and an `apiKey` instead of a `username` and `password`:

```js
// This:
const apiConfig = new Configuration({
  clientId: process.env.MX_CLIENT_ID,
  apiKey: process.env.MX_API_KEY,
})

// Instead of this:
const apiConfig = new Configuration({
  username: process.env.MX_CLIENT_ID,
  password: process.env.MX_API_KEY,
})
```