Follow symlinks during sdist generation

[vyasr]

For packages contained in monorepos it can be convenient for certain files within a Python package to simply be symlinks to a common version in the root of the repo (licenses, readmes, etc). It may also also be important for other reasons, such as if different language implementations and bindings are maintained in a flat folder structure. scikit-build classic (i.e. setuptools) will traverse symlinks when building an sdist and copy in the full file. scikit-build-core appears to retain symlinks as is, which can result in invalid sdists containing invalid symlinks (pointing outside the package). Following symlinks would help support this use case.