[Feature] Support badges of latest version on your package server (`pkg.pkl-lang.org`)

[StefMa]

I want to add a badge to my README file that shows the latest version that consumers can use. Similar to other badges supported by https://shields.io

I guess a Pkl server requires to send the latest version if requested with latestor something so shields.io (or others) can use that API to display the latest version.

Its a bit related/similar to https://github.com/apple/pkl/issues/278 or better to this comment.

If you support using e.g. package://pkg.pkl-lang.org/github.com/stefma/pkl-gha/com.github.action@latest and this would redirect to the latest version (0.0.1 🤷), then it would be possible to implement... I guess 😁

Also not sure if this issue should be better placed at https://github.com/apple/pkl-lang.org 🤷 Feel free to move it.