Allow selection of subworkflow versions

[simonbray]

There is currently a really nice feature allowing users to upgrade to the latest version of a subworkflow in the workflow editor:

I think this would be more intuitive and more useful if it worked exactly the same as a tool version change, i.e. if clicking the stacked boxes icon produced a dropdown menu with all subworkflow versions available.

[simonbray]

I think it's basically the same as the {action: 'restore_workflow_version'} proposed in #11005.