doc: contribute: Extend Reviewer Expectations with additional rules

This change was triggered by a review comment linked below:
https://github.com/zephyrproject-rtos/zephyr/pull/83117#issuecomment-2549120181



It extends the current Reviewer Expectations with additional rules
agreed upon by multiple Zephyr contributors in order to simplify and
standardize the decision-making process during PR reviews.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
Signed-off-by: Anas Nashif <anas.nashif@intel.com>