Provide a license report

At the moment, it is hard to generate a bill of materials for dependencies. Since IIUC standard Haskell practice is to link statically, that seems to mean that binary distributions effectively are redistributing derivative works of all dependencies, and so my understanding is that all their license terms need to be distributed along with the software.

However, I acknowledge that even projects as conservative as Debian [aren't bothering to do this][debian-licensing], so this may be a solution looking for a problem. On the other hand, the existence of [`cabal-plan license-report`][cabal-plan] suggests to me that some people are bothering to do this.

In particular `stack ls dependencies --license` isn't enough. This is for a couple of reasons:
- For some licenses (MIT, BSD, ISC, ...), the license text needs to also be distributed.
- The output still needs to be massaged into an actual report
- It'd be nice if the report could canonicalize the license strings -- right now it seems it produces the raw license strings from the `.cabal` files.

(A further ask that requires social, not technical, solutions is to have the license strings be SPDX identifiers, since the current freeform standard gives rise to such ambiguities as "What does `GPL` mean?" (version is ambiguous, as is whether using later versions is permitted))

Hacking a solution around [cabal-plan] is not viable, since it requires both a `plan.json` (which might be generated from a freezefile, but…) and also a populated Cabal store. Hence, a `stack`-native solution is necessary. For the same reason, it is unreasonable to push this to [cabal-plan], and given that `stack ls dependencies --license` exists, it makes sense to push for it to actually be useful.

[cabal-plan]: https://hackage.haskell.org/package/cabal-plan
[debian-licensing]: https://lists.debian.org/debian-legal/2023/09/msg00001.html