cmake: initial version of a CMake yaml module

Initial CMake yaml module to facilitate reading yaml files into CMake,
update yaml settings and write it back to a file.

The yaml module also supports creation of yaml files from scratch.

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

share/sysbuild/cmake/modules/sysbuild_default.cmake

@@ -9,6 +9,7 @@ include(extensions)
 include(sysbuild_extensions)
 include(python)
 include(west)
+include(yaml)
 include(sysbuild_root)
 include(zephyr_module)
 include(boards)