virsh: Added attach-disk support for network disk

virsh: Added attach-disk support for network disk

Related issue: https://gitlab.com/libvirt/libvirt/-/issues/16
Added in support for the following parameters in attach-disk:
--source-protocol
--source-host-name
--source-host-socket
--source-host-transport

Added documentation to virsh.rst specifying usage.

Signed-off-by: Ryan Gahagan <rgahagan@cs.utexas.edu>
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>