fix: use ubuntu:23.04 as base image

[alambike]

• Use ubuntu:23.04 as base image, as its the minimum image with upbound 1.14.
• Reconfigure unboundtest to b able to use unbound.conf from /etc/unbound

[jsha]

Sweet, thanks for the fix! I was actually just working on updating the Dockerfile to use 23.04 (lunar).

I'm not so sure about the other changes. Why pull from /etc/unbound? For local dev outside a container I've found it convenient to pull from a file in the current directory. Similarly, why run as root? I'd actually love for this to be able to run in a rootless Docker setup.

Also, the diff to remove IPv6 support is incorrect for this repository's intended use.

Out of curiosity, can I ask what you're using this code for?