Prompt to update package list instead of proceeding

When running any of the cabal commands I quite often get either that the package list is old or (as I currently did on a fresh machine) that it doesn't exist:
```
Warning: The package list for 'hackage.haskell.org' does not exist. Run 'cabal
update' to download it.
Resolving dependencies...
Error: [Cabal-7107]
Could not resolve dependencies:
...
```

Instead of just proceeding, display a prompt `Do you want to download or update the package list? (y/n)` instead. Especially if the package list doesn't exist. Otherwise, as the build proceeds and more output is written to the console, if the user is not careful to read it, they might not notice that the package is actually buildable, but it's just the package index that is missing.