Would be nice to have assume (similar to expect) for E2E tests

Motivating example:smiley::

```js
const userRes = await sdk.addUser({ email: 'john@smith.com' }).assume(200)
const loginRes = await sdk.login({ username: 'john', password: 'smith' }).assume(200)
const accessToken = loginRes.body.acessToken

await sdk.order({ quantity: 42, item: 'rubber-duck' }).expect(200)
```

In this case I'm testing the order bit and only assumes the steps before are successful:sweat_smile:.