scripts: extend west build command to support sysbuild CMake project

west build now support the sysbuild CMake project which allows users
to easily enable and build a bootloader together with any sample.

This will allow for cleaning up samples and boards which already does
custom multi image in a non-generic way, for example:
- mps2_an521 which includes a build for remote board
- samples/ipc/ which includes a samples for remote board
- esp32 which includes custom bootloaders

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>