Support for full static workflow

[traversaro]

For embedded use cases, it would be cool to be able to just compile qpsolvers-eigen and all its dependencies as static libraries, and be able to use them without problems. Probably this requires some modification also to sharedlibpp, but it should be doable.

Definition of done (just an example, but I think it would be a good use case), this should work fine and the resulting QpSolversEigen-SimpleExample should be a self-contained executable:

./vcpkg --install qpsolvers-eigen[osqp,proxqp] --triplet x64-windows-static
git clone https://github.com/ami-iit/qpsolvers-eigen
cd qpsolvers-eigen/examples/simple
cmake -GNinja -Bbuild -S. -DCMAKE_TOOLCHAIN_FILE=$env{VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake"
cmake --build build
cd build
.\QpSolversEigen-SimpleExample