doc: coding guidelines: Add a new rule for macro name collisions

This commit is the outcome of the discussion that has taken place in
multiple forums:

Discord:
https://discord.com/channels/720317445772017664/1014241011989487716/1032623375228608522

GitHub:
https://github.com/zephyrproject-rtos/zephyr/issues/51371
https://github.com/zephyrproject-rtos/zephyr/pull/50239



Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>