tests: mcuboot: pytest: Add image swap test with mcumgr

Added application based on SMP Server Sample. Application is built together
with MCUboot using sysbuild and is flashed onto device in one step.
Tests are automated with pytest - new harness of Twister.
The image for upgrade is prepared using west sign command
then is uploaded by mcumgr into device and tested.
Automated scenarios to test upgrade (image upload, test, revert, confirm),
to test downgrade prevention mechanism and to test upgrade with image,
that is signed with an invalid key.

Signed-off-by: Grzegorz Chwierut <grzegorz.chwierut@nordicsemi.no>