Do we need post actions?

The previous middleware pipeline allowed actions to be performed both before and after the next step in the middleware pipeline. As we replace that pipeline with CliAction we made a change to accomodate pre-actions that come before the selected command's action runs. These are called non-exclusive actions in #2147.

We are considering whether to support post actions. Current argument set:

* For: We had this capability prior to the redesign, and someone may have used it
* For: There is a nice symmetry
* Against: We do not have an actual scenario

So, if you were doing things in a custom middleware step after the next step returned, please let us know!