samples: sysbuild: with mcu_boot on the stm32h573i_dk

Run the sample to execute in place on the external flash of the
stm32h573 disco kit.
with_boot is build and linked for the external flash.
Download the mcuboot zephyr.bin in internal memory.
Download the with_mcuboot zephyr.signed.bin in external memory.

Signed-off-by: Francois Ramu <francois.ramu@st.com>