etcd images: aspect of licensing/busybox

[ptabor]

What would you like to be added?

Follow up to #13556

Currently we generate images based on:

FROM --platform=linux/s390x busybox:1.34.1 as source
FROM --platform=linux/s390x gcr.io/distroless/base-debian11
...
RUN mkdir -p /var/etcd/
RUN mkdir -p /var/lib/etcd/
...
RUN echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf

CMD ["/usr/local/bin/etcd"]

Seems that:

1. We can use https://docs.docker.com/engine/reference/builder/#workdir to get rid of MKDIR
2. We can copy the /etc/nsswitch.conf to avoid need for echo and bash redirect syntax (>>)
3. I don't see other reasons to keep /bin/sh
4. As etcd is statically compiled, we might not need base-debian11 image at all

Why is this needed?

To isolate from security and licensing problems.

[ahrtr]

Done.