Have something like "stack install --use-stack-yaml-from hackage-pkg"?

For situations like https://github.com/commercialhaskell/stack/issues/2039 , where the user does `stack install a-non-stackage-hackage-package`, the issue is that we don't know what package versions to use for things outside our resolver. As discussed in that issue, one way to resolve this is to support a `--solver` flag and create a temporary sandbox for this particular build.

Another approach might be to actually just use the stack.yaml included with the package, if it exists. This
might be a reason to include it by default in sdists: https://github.com/commercialhaskell/stack/issues/2105

This way we can directly tell the user how the package author intended for it to be installed.

Open questions: What about multiple stack files?