Merge branch 'feat/upgradetobookworm' into 'main'

upgrade runtime container from s6-base deb11 -> s6-overlay-lite deb12, openvpn from 2.5.1 -> 2.6.3

See merge request !8

Dockerfile

-FROM debian:bullseye-backports AS build
-RUN apt-get -q update \
-  && DEBIAN_FRONTEND=noninteractive apt-get install -qy --no-install-recommends \
-  build-essential \
-  pkg-config \
-  git \
-  ca-certificates \
-  golang-1.19-go \
-  && rm -rf /var/lib/apt/lists/*
-
-ENV GOPATH=/go
-WORKDIR $GOPATH
-
-FROM registry.git.autistici.org/ai3/docker/s6-base
+FROM registry.git.autistici.org/ai3/docker/s6-overlay-lite:v12.0.0
 
 COPY kresd.key /usr/share/keyrings/kresd.gpg
-RUN echo "deb [signed-by=/usr/share/keyrings/kresd.gpg] http://download.opensuse.org/repositories/home:/CZ-NIC:/knot-resolver-latest/Debian_11/ /" > /etc/apt/sources.list.d/kresd.list
+RUN echo "deb [signed-by=/usr/share/keyrings/kresd.gpg] https://download.opensuse.org/repositories/home:/CZ-NIC:/knot-resolver-latest/Debian_12/ /" > /etc/apt/sources.list.d/kresd.list
 
 RUN apt-get -q update \
   && DEBIAN_FRONTEND=noninteractive apt-get install -qy --no-install-recommends \