cli: workflow diff
cli: workflow diff

* Adds diff command returning the differences between two workflows.
  Includes optional flags to show short diff or full extensive diff,
  including differences in the file contents between the two
  workflow workspaces.

Signed-off-by: Dinos Kousidis <2232407337c30afa275b4ef42b0b26111a2f9dfc@cern.ch>

reanahub/reana-client,reanahub/reana-client