Make sure config_checkpoint_ui is not uninstalled

Problem/Motivation

it is possible to revert to a checkpoint from before the module is installed, which would uninstall the module in the process, this would be quite "fun".

Steps to reproduce

apply a recipe which creates a checkpoint, install the ui module, revert to the checkpoint, ui and its routes are now gone.

Proposed resolution

Ensure that the checkpoint ui module remains installed.
This means that we don't exactly revert to the sate of the checkpoint, but this is an acceptable tradeoff when the other option is to break the process in the UI.

Remaining tasks

patch

User interface changes

none

API changes

none

Data model changes

none