I want to create groups of imported files so they are all updated together

For example, files scattered throughout a repo for implementing formatting, imported from another Git repo.

```sh
fromwhere pull group my-formatting-files
```

Start by tracing the `fromwhere pull` CLI entry point and reviewing how imported files are currently represented and updated. Define how a named group such as `my-formatting-files` would identify scattered files from another Git repository, then verify that one group update changes all of its files together.

Written by the indexing model from the issue text.