Register kubernetes extension

[lordofthejars]

When running ./mvnw quarkus:list-extensions you see a lot of extensions but one that is set in guides but not registered is the one about Kubernetes.

io.quarkus:quarkus-kubernetes

I am using Quarkus 0.13.1

[lordofthejars]

I can help with a PR.

[gsmet]

Look for extensions.json in the tree, you need to add an entry here (if not already done in master). They are ordered alphabetically.

Thanks!

[geoand]

Funny, I remember adding this.... I guess it must have got lost in the many rebases/squashes that were done during the development of the extension.

Thanks for spotting!