Proposal: make raise_for_status chainable

[trim21]

make it possible to write code like r = httpx.get('...').raise_for_status().json()

[karpetrosyan]

Hey! I moved your issue to discussion because that is where ideas like this start, and if it is approved, we can move forward by opening an issue.

[tomchristie]

See pull request #2776.

(Reminder to all... let's start with escalating to an issue if a discussion is accepted, rather than jumping straight to a PR.)

Anyways... great thanks!