osbuilder: Evaluate whether makes sense to keep supporting the alpine rootfs

[fidencio]

This is part of a bigger effort to simplify what we support and ensure we actually test what we say we support.

The outcome of this should be:

• Whether we support or not the alpine rootfs
• Where do we use the alpine rootfs
• Who's the person responsible for maintaining the alpine rootfs

All the information will end up going to a Wiki page so we can actually act whenever an issue shows up or an update has to be made.

[Jakob-Naucke]

FYI it can't even work on s390x (and ppc64le probably?) because you can't run a binary built against glibc on Alpine, and there is no Rust target for the agent on those platforms