RFC: API Change: mgmt: mcumgr: transport: Add query valid check function

McCrae, Jamie

I have submitted an RFC for a stable API change in MCUmger to add a new function pointer that adds functionality to transports to check if pending queries are still valid or if they are invalid and should be dropped. This addresses an issue with queued commands being wrongly processed if the device that sent them disconnects. RFC link: https://github.com/zephyrproject-rtos/zephyr/issues/52022
This would affect applications applications registering custom MCUmgr transports, a NULL function pointer needs adding to non-connection based transports, or the callback functionality needs implementing for connection based transports.