Apparently,

````
quarkus create --gradle -x quarkus-amazon-lambda-http
cd code-with-quarkus/
./gradlew addExtension --extensions=jackson

> Task :addExtension
👍 Extension io.quarkus:quarkus-jackson was already installed
````

Although `quarkus-jackson` isn't a direct dependency in the build script but a transitive one.

@glefloch could you please review this one? This code isn't exactly correct, because I couldn't get to the actual artifacts. I guess I would need to actually resolve the configuration to get them, which is unfortunate.