Ship static busybox shell in container-toolkit image

Flip the packaging and application stage bases from *-dev* to
non-*-dev* distroless and source a static busybox from
debian:trixie-slim. Build-time RUN commands and the application
entrypoint continue to work via /bin/sh and busybox applet symlinks.

Part of NVIDIA/cloud-native-team#299.

Signed-off-by: Rajath Agasthya <ragasthya@nvidia.com>