* vpn: ship our own container image
The container image used in the VPN chart should be reproducible and
stable. We're sticking close to the original nixery.dev version by
building the image with nix ourselves, and then publishing the single
layer from the result with Bazel OCI rules. The resulting image should
be handled similar to s3proxy: it's built as a part of the Constellation
release process and then consumed from a Helm chart in our registry.
Co-authored-by: Malte Poll <1780588+malt3@users.noreply.github.com>