Support `store-dir` and `package-env` in `cabal.project`

**Describe the feature request**

It seems like an oversight that these aren't supported. I would have expected that `cabal.project` is kind of a superset of `cabal.config`.

I don't really see any problems allowing them to be set at the project level. It actually seems kind of intuitive to do so.

**Additional context**

This is needed to implement a prototype for cabal sandboxes, see: https://github.com/haskell/cabal/issues/10098

Start by comparing the existing handling of `store-dir` and `package-env` in `cabal.config` with the project-level behavior expected from `cabal.project`. Review the linked cabal sandbox prototype in issue #10098 for context. Done means both settings are accepted and work at the `cabal.project` level.

Written by the indexing model from the issue text.