Feature request: set origin

would be awesome to cover allowed origins, i.e.:

```
// app.js
app.get('/', cors({
origin: "http://allowed.com"
}), (req, res) => {
res.sendStatus(200)
})

// app.spec.js
const resp = await supertest(app).post('/').origin('http://allowed.com')
expect(resp.status).toStrictEqual(200)
```