Replace the `SSH` class by a Python library?

As explained in https://github.com/DIRACGrid/DIRAC/pull/7025, the ` _ssh_call()` method does not seem to work perfectly.
There exist a few popular python libraries to perform SSH operations like `Fabric` (Paramiko) (https://docs.fabfile.org/en/stable/).

We could investigate the possibility of using one of them instead of relying on our `SSH` class to perform remote operations over SSH. 
