The default cabal config file specifies some directories explicitly, but not all, nor none.

E.g. I can see (on a fresh machine, after `cabal update`):

```
-- store-dir:
-- active-repositories:
-- local-no-index-repo:
remote-repo-cache: /home/phadej/.cache/cabal/packages
-- logs-dir: /home/phadej/.cache/cabal/logs
...
build-summary: /home/phadej/.cache/cabal/logs/build.log
```

I don't understand the reasoning why `remote-repo-cache` is explicitly specified, but `store-dir` and `logs-dir` aren't.

I'd expect all or none.