feat(docker): use host system timezone instead of hardcoded Europe/Dublin

[taraxacum45e9a]

All Dockerfiles had TZ hardcoded as ENV TZ="Europe/Dublin", which baked the timezone permanently into the image and made it non-overridable at build time.

This changes TZ to a build ARG (defaulting to Europe/Dublin for backwards compatibility) and passes the host's timezone via --build-arg TZ=$(cat /etc/timezone) in run-with-docker.sh, so containers reflect the system timezone of whoever is building them.

[amd-vserbu]

Agree with the change, but there are two issues:

1. /etc/timezone is a Debian-ism, so the package script would now fail when run from RHEL. Better would be: --build-arg TZ="$(timedatectl show -p Timezone --value)" which should work on anything systemd.
2. ARG only inserts the variable in the build environment, but not in the final runtime environment. This is a quick fix with:

ARG TZ="Europe/Dublin"
ENV TZ="${TZ}"

[quetric]

@taraxacum45e9a thanks for your contribution. Please see Vlad's requests and update the PR to progress.

[taraxacum45e9a]

Thanks for the suggestion. I don’t have RHEL locally, so I wasn’t able to validate on that OS, but I’ve updated the script accordingly.

Regarding the ENV TZ point — since the timezone is already applied during build (via linking /etc/localtime and writing /etc/timezone), the runtime environment should already reflect the correct timezone. Given that, setting ENV TZ again seems redundant.