provide debug runner image

[freeznet]

nonroot runner image cannot install debugging tools, which makes the debug much more harder than before. We should provide a debug image with all tools available, or provide a root user version.

[hpvd]

if already an independent debug image is needed, one may take the chance to look into to

• stripdown the main image further to completely distroless
  and
• go/propose for debugging the ephemeral container route

for an overview on this topic see #448