feat(cli): add 'command' column to 'renku workflow ls'

[Panaetius]

closes #2334

Use like

$ renku workflow ls
ID                                       NAME             COMMAND
---------------------------------------  ---------------  -------------
/plans/11a3702184394b93ac422df760e40999  cp-B-C-ca4da     cp B C
/plans/1cc6d33b48ef4d13bf5b1f441b286397  cp-CC-DD-fab0c   cp CC DD
/plans/1e36a9ff580d49cda5f3f8fbf8224b53  cat-Z-C-E-c6bbf  cat Z C E > n
/plans/286c1a56342d4a9c9f03f62ff18e4b0e  cat-Y-Z-1b5ab    cat Y Z > M
/plans/2a6b5588f52d4579bac46f3a5bfc8fbb  cat-B-D-bd7eb    cat B D > E
/plans/2a6db7a35f47499dbce56ae55c2b725d  cp-BB-CC-a3ad0   cp BB CC

or

$ renku  workflow ls -c command
COMMAND
-------------
cat A C > D
cat B D > E
cat Y Z > M
cat Z C E > n
cp A B
cp B C
cp BB CC
cp CC DD
cp X Y
cp X Z
cp bla CC