fix: define all build args at the top of the Dockerfile

[eeberhard]

Description

Fix following build failure here:

• https://github.com/aica-technology/docker-images/actions/runs/9061701641/job/24894045916

Build args need to be declared at the top layer, otherwise they might be skipped in intermediate layers and remain undefined. As part of this, I removed the secondary declarations of the build args in the later layer.

Review guidelines

Estimated Time of Review: 1.1 minutes

Checklist before merging:

• Confirm that the relevant changelog(s) are up-to-date in case of any user-facing changes

[LouisBrunner]

This is incorrect and actually breaks the metadata:

                "devcontainer.metadata": "[{\"containerUser\": \"ros2\"}]",
                "org.opencontainers.image.base.name": ":",
                "org.opencontainers.image.description": "AICA base ROS 2 image (includes ros2_control)",
                "org.opencontainers.image.ref.name": "ubuntu",
                "org.opencontainers.image.title": "AICA ROS 2 image",
                "org.opencontainers.image.version": "",
                "tech.aica.image.metadata": "{\"type\":\"base/ws\",\"base\":{\"name\":\"${BASE_IMAGE}:${BASE_TAG}\",\"version\":\"${VERSION}\"}}"

Stages only inherit the ARG from the stages they inherit from and top-level ARG are seemingly only associated with the first stage, resulting in empty metadata (some is also badly formatted, introduced in #109 (comment)).