doc: harden policy around objections

Harden policy around objections to avoid misunderstanding and to
encourage collaboration between pull request authors and objectors.

Fixes: https://github.com/nodejs/node/issues/34564

PR-URL: https://github.com/nodejs/node/pull/34639


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>