Files primed from the static folder can have different permissions depending on umask

Files primed from the static folder can have different permissions depending on umask, as git clone set permissions depending on it (git repositories don't track file modes, other than the executable bit and whether the file is a symbolic link: https://git-scm.com/book/en/v2/Git-Internals-Git-Objects#_tree_objects). Therefore, to have reproducible builds we should use probably `install` on those files instead of `cp -a`.

See also `core.sharedRepository` in https://git-scm.com/docs/git-config.