Add badge endpoint for each extension

[holly-cummins]

Suggestion from @maxandersen.

For example, https://quarkus.io/extensions/io.quarkiverse.jgit/quarkus-jgit/badge/3.3.2. It would return an image with basic info that links to right places. Supporting multiple versions with the current architecture would be hard, so https://quarkus.io/extensions/io.quarkiverse.jgit/quarkus-jgit/badge/latest might be a better starting point.

This is related to #175 but wraps the image in a link.