Code review comment for ~bdrung/autopkgtest-cloud/+git/autopkgtest-package-configs:sort

This currently doesn't work due to comments in `big_packages` (yes, they are supported [1]).
Steve's comments about the `python3-natsort` dependency still stands.

I'll add:
- ideally, introducing any kind `sort` script should come with enforcing it in the CI
- any decent text editor has a `sort` function too

[1]: https://git.launchpad.net/autopkgtest-cloud/tree/charms/focal/autopkgtest-cloud-worker/autopkgtest-cloud/worker/worker#n275