quic: refactor clientHello

Refactor the `'clientHello'` event into a `clientHelloHandler`
configuration option and async function. Remove the addContext
API as it's not needed.

PR-URL: https://github.com/nodejs/node/pull/34541


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>