Fix example build

[ToKiNoBug]

I see 2 example tests in "C++ Test" action failed after merging my PR.

It was caused by CMAKE_SOURCE_DIR in file cmake/set_package_info.cmake to access readme and license files. It seems ok beacuse they works almost the same as PROJECT_SOURCE_DIR, but in example builds CMAKE_SOURCE_DIR points to examples/logistic_regression , however license and readme files are not located here.

So I replaced CMAKE_SOURCE_DIR with PROJECT_SOURCE_DIR to fix this.

The cpp_example gh action is also changed.
Before this, cmd line parameter KOMPUTE_OPT_FROM_SOURCE=ON doesn't start with a -D prefix, so it will be ignored without any warnings and the value of KOMPUTE_OPT_FROM_SOURCE is still false.
As a result, example builds will still access kompute from the remote master branch instead of the parent directory. I have to fix this, otherwise gh actions will always fail.

[axsaucedo]

Thank you for the contribution