Harbor dockerhub-cache proxy handles Docker Hub pulls without
needing direct Docker Hub authentication. Removes the failing
index.docker.io login blocks from all build pipeline steps.
The plugin-docker-buildx inherits proxy env vars from the pod/node.
Setting http_proxy/https_proxy to empty strings overrides any
inherited proxy config so Docker can reach Harbor directly.
Buildkit resolves registry hostnames using its own resolver which
doesn't use the custom_dns setting. Adding an explicit host entry
ensures registry.celestium.life resolves even when cluster DNS
can't reach the proxy DNS.
Celes Renata