Support for pkl

[StefMa]

It would be great if this library has support for apples "new" configuration language pkl.

Some info can be found here:
apple/pkl#849

[knadh]

Perhaps we should close this as the aforementioned thread confirmed the hard dependency on the external pkl binary?

[StefMa]

What's wrong with having the pkl binary as a dependency? 🤔 Sure not the most elegant solution, but if someone wants to use that 🤷‍♂️.

If you are against it, also fine for me. However, we might can also keep it until they lift the restriction with the binary? 🤔

[knadh]

While koanf is agnostic to whatever happens in a provider, given that the pkl ecosystem (eg: docs) itself doesn't lend much clarity on how it works, feels a bit off ship a provider that has an external bin dependency.

That said, it's not a big deal. If you'd like to send a PR (which can clearly document that it requires the pkl bin to be installed), then it's fair enough I guess.