demo/compose: Add proxy config for build
demo/compose: Add proxy config for build

When behind a proxy, we need proxy env variables
for the build stage.

Signed-off-by: Spyros Trigazis <1e6dbf5402ced737cda15d668682ea874352489e@cern.ch>

containerd/stargz-snapshotter,containerd/stargz-snapshotter,containerd/stargz-snapshotter,containerd/stargz-snapshotter