Update documentation for worker UI redesign

The new worker UI in frontend!1839 (merged) implies updating every screenshot of the worker version selection modal, the worker list page, and the worker details page. The recommended versions documentation in !212 (merged) also needs to updated.

changed milestone to %Arkindex 1.7.2

added P2 label

assigned to @erouchet

mentioned in merge request !215 (merged)

closed with merge request !215 (merged)