Support other cloud providers

If this image were to become the official image for upstream Alpine, we'd need to support more than just AWS. After talking to the Alpine developers, they consider these cloud providers to currently be high priority for their images (there may be others later).

Making these work will require open sourcing and significant expansion of the identity broker (doable with some time) as well as a lot of re-tooling work for the release process. It might make more sense for us to move a lot of that into the identity broker and keeping the Python scripts a build-only concern.

This issue exists more to document my thoughts and conversations with upstream, and to collect public opinions than something that can immediately be worked upon.

Edited Apr 16, 2023 by Jake Buchholz Göktürk