Add file patterns to config.json

[ErikSchierboom]

To help tracks define the files in the exercise's .meta/config.json file, we've added support for defining these file patterns in the track's config.json file. See this PR.

We'll send PRs to update the file paths defined in the files property of each exercise's .meta/config.json file according to the file patterns defined in the track's config.json file.

We only update a file path in the .meta/config.json file if:

• The file path pattern is a non-empty array in the config.json file
• The file path pattern is either not set or an empty array in the .meta/config.json file

This means that exercises that had already defined files in the .meta/config.json won't be touched in the PRs.

Note that these PRs are just an easy way for tracks to populate the files in the .meta/config.json files. Tracks are completely free to add/change/remove the files in their .meta/config.json files.

In the future, we'll update configlet to include this functionality. If you'd like me to re-run the script because changes have been made to your track, feel free to ping me on Slack (@erikschierboom).

[ErikSchierboom]

There are five open PR's, but none of those tracks (z3, system-verilog, forth, io, nix) have exercises. So I'm comfortable closing this.