samples: subsys: mgmt: smp_svr: add udp sample

This sample now supports SMP UDP transport.
Two config overlays have been added for ipv4 and ipv6, respectively.

The sample documentation has been completely revamped to be less
bluetooth focused and more general.

Signed-off-by: Mikkel Jakobsen <mikkel.aunsbjerg@prevas.dk>
7 files changed