WIBNI: edit data file for installed program

**Describe the feature request**
Simple ability to list and/or edit data files for installed programs

**Additional context**
`data-files` live in cabal's store, for very good reasons. But this makes them not very discoverable when someone needs to edit one.

I propose a new command `cabal [v2-]edit [--list|]` (the default action would be to list, `--list` would just make it explicit) to show or edit such files. The guts of this wouldn't be much different from `cabal install` with a package already installed into the store.

Whether it would do anything useful for a package not already installed would be something to discuss before implementation: on the face of it it doesn't look very useful, but on the other hand it's probably difficult to not have cabal install the requested package/version when it's not already present.