Added cmake options to include framework in external projects

CMakeLists.txt

config/ext/Doxygen.cmake

modules/CMakeLists.txt

modules/asset_loader/CMakeLists.txt

modules/camera/CMakeLists.txt

modules/gui/CMakeLists.txt

modules/material/CMakeLists.txt

modules/meshlet/CMakeLists.txt

modules/scene/CMakeLists.txt

modules/shader_compiler/CMakeLists.txt

modules/testing/CMakeLists.txt

modules/upscaling/CMakeLists.txt