Allow post-job actions to be set for subworkflow outputs

Concretely, I would like to be able to rename a subworkflow output. Surprised that there isn't an existing issue, or at least I couldn't find one.

For tools I see this:


but for subworkflows this:


No files, tests, or entry points are identified in the issue. Compare how post-job actions are handled for tool outputs with the corresponding subworkflow-output path, then trace the subworkflow output handling from there. Done means a subworkflow output can be renamed through the same kind of post-job action available for tools.

Written by the indexing model from the issue text.