[Feature request] Support overriding `main`, `exports` and other package.json fields with `publishConfig`

[remorses]

Currently publishConfig can only override .npmrc fields, other package managers like yarn and pnpm instead let you override exports and main for example.

Adding support for this feature would allow using typescript files in development and javascript dist files when publishing, making package development much easier. https://github.com/isaacs/tshy/issues/65

It would also make npm behaviour consistent with other package managers.