RFC: API Change: watchdog: wdt_feed error codes

Peter A. Bigot

The API change proposed here and summarized below has been completed.

Following https://docs.zephyrproject.org/latest/development_process/api_lifecycle.html#stable we have a need to make a small change to the watchdog API that meets the criteria of "...forces users to modify their existing code in order to maintain the current behavior of their application".

Please see: https://github.com/zephyrproject-rtos/zephyr/issues/26708