sysbuild: Adding other modules required for a sysbuild example

<!-- ps-id: 0528eaef-3719-4c12-b291-60e1cb602406 -->

Author: jameswalmsley

west.yml

@@ -20,3 +20,4 @@ manifest:
           - cmsis_6    # required by the ARM port for Cortex-M
           - hal_nordic # required by the custom_plank board (Nordic based)
           - hal_stm32  # required by the nucleo_f302r8 board (STM32 based)
+          - mcuboot