release vaultenv to Hackage

It would be convenient for Linux distributions if vaultenv were released to Hackage.

There is already an issue about this (#1), but it has been closed with this last comment:

> If anyone sees this and has requests wrt to the release process, please open a new ticket

One thing that wasn't mentioned in #1 is that uploading to Hackage can sometimes help Linux distributions package vaultenv.

Some Linux distributions (including NixOS) have an automated process for building and updating Haskell packages that are uploaded to Hackage.

Since vaultenv is not uploaded to Hackage, it has to be updated by hand.

This isn't difficult, but it is a manual step we have to perform. vaultenv is sometimes out of date because no one realizes it need to be updated. If vaultenv was on Hackage, then we wouldn't have to do this.

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Also, uploading packages to Hackage is relatively easy for the maintainers of the package (just `stack upload`), so hopefully it wouldn't be imposing too much.

(Although, there are other well-known packages that choose not to upload to Hackage. For instance [spago](https://github.com/purescript/spago) is one I know well. So it is not like it is completely unheard of not uploading to Hackage.)