> Can you show me an example of such a package?

https://github.com/magnars/dash.el

> All the Elpa packages are hosted on a Savannah instance.

That's the "publishing repository". You have to push there for a new version of your package to be published on GNU Elpa. But for most packages development happens elsewhere, and in most cases "elsewhere" is Github. Emacs maintainers sometimes commit directly in the Elpa repository (and package maintainers are expected to deal with the consequences, such as "two diverging mainlines"), but development happens elsewhere.