mark config changesets as being in-progress

This might require some planning, but the goal is to indicate in the UI that a merge of config changes has been initiated. There may be some lag between initiating a patch and the config is deployed to the codebase as a merge request is reviewed or CI is running (when the deploy is complete the status is clear because the config diffs go away).

I'm thinking the pieces of this would include:

- uniquely identifying individual config items
- tracking the changeset (collections of config submitted in a patch), probably in a simple DB table or maybe as entities
- a URL callback for external systems to indicate the status of a changeset ("received", "under review", "in progress", "building" -- etc. etc.)
- garbage collection once config is in sync