west: runners: Add ncs-provision to west flash command

Added automatic KMU key provisioning, when keyfile.json
file exists in the build directory.
This enables automated key provisioning during the
flashing process to enable testing nRF54L aplications using Twister.
Only applicable on nrfutil runner.

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