doc: add parameters for Http2Session:stream event

Add parameters for the callback for the Http2Session:stream event
inline with the pattern in the rest of the documentation.

Refs: https://github.com/nodejs/help/issues/877#issuecomment-381253464

Backport-PR-URL: https://github.com/nodejs/node/pull/22850
PR-URL: https://github.com/nodejs/node/pull/20547


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>