net: lwm2m: Add config to always report obj version

Adds a config that enables sending the object version for all objects.

According to LwM2M specification v1.0 and v1.1, non-core object versions
other than 1.0 'must' be provided, while all other versions 'may' be
provided. With specification v1.2, a client 'can always attach Object
Version Information'. Or in other words, it is OK to always report the
object version with all specifications.

Signed-off-by: Andreas Rudolf <andreas.rudolf@husqvarnagroup.com>