- Added CPM fallback in case package is not found automatically.
 - Using yaml-cpp::yaml-cpp target instead of yaml-cpp to silence deprecation
   warnings on newer cmake versions.

This commit adds yaml-cpp library to required docker images and build commands. There is one workaround
in cross-compilation for apt behavior for installing libyaml-cpp-dev. Apt will uninistall previous
versions of the package whenever another one is installed. This means that installing the arm version
breaks amd version and vice versa. This makes it impossible to have both libs installed at the same
time which is required by the cross-compilation build command (it calls cmake twice, once with native
and once with target architecture)

This commit introduces a substitute module library for setting up softmodems using YAML instead of libconfig.
The softmodems should work the same with both types of files. Extra care was put to make sure the behavior
of both modules is the same.

Example yaml config files were added for the UE and gNB