I noticed new extensions are still being created with a docs url of the form http://quarkiverse.github.io/quarkiverse-docs. We should prefer the https://docs.quarkiverse.io url, partly because it's shorter and prettier, but also because it's not coupled to a hosting provider.

I started out fixing just the extension templates, but then I decided that while I was searching I'd change the other occurrences, too.