Use extension shortId when sending request to code.quarkus.io

When lots of extensions are selected, the computed URL is too long and request to code.quarkus.io. The backend implemented the notion of shortId (see https://github.com/quarkusio/code.quarkus.io/commit/20e041e7006f3bbecfe27d2896d8dd1ece9d6fe7) so that the URL length is shortened