cmake: sysbuild PRE_CMAKE, POST_CMAKE, PRE_DOMAINS, POST_DOMAINS hooks

Provide a uniform way for sysbuild modules to create hooks that are
called at specific time during sysbuild CMake configure time.

A module can create functions following the scheme:
- <module-name>_pre_cmake
- <module-name>_post_cmake
- <module-name>_pre_domains
- <module-name>_post_domains

those functions, if defined, will be called by sysbuild CMake at the
location indicated by the function name.

A new global variable `SYSBUILD_CURRENT_MODULE_NAME` is created, which
a module can use to know it's own name when defining those functions
during sysbuild module CMake inclusion.

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