Overlink I/O: Create Symlinks

[JustinPrivitera]

Users are running into this. We should create the symlinks when we write Overlink files. We should figure out the platform-specific issues (i.e. how can we do this on Windows?).

[cyrush]

We should add a helper to conduit utils https://github.com/llnl/conduit/blob/develop/src/libs/conduit/conduit_utils.hpp

We could use std filesystem if we require c++17, but there are also platform specific calls we can use.