Try hard linking netCDF files to workspace folder instead of copying

[nbercher-atk]

Expected behavior

dedop should try to make hard links of input netCDF files instead of copying them to the workspace when:

1. on a Unix-like system,
2. workspace and source L1A files are on the same data volume (otherwise hard linking is impossible to do).

Alternatively, dedop could set up symbolic links on Unix-like systems or shortcuts (if judged reliable) on Windows systems. For Windows shortcuts & Unix-like symlinks, this should be triggered by a new dedop option to the =dedop input add files= command (e.g. "--links" option).

Actual behavior

dedop always copies files resulting in disk space waste.

Steps to reproduce the issue

Make a workspace and add inputs files to it.

Specifications

This request concerns only Linux & Unix-like users and maybe MACOSX users.