Investigate registry mirror proxy for non docker hub registries.

[GrahamDumpleton]

Is your feature request related to a problem? Please describe.

Apparently one can use docker registry as caching proxying for registries besides docker hub.

docker run -d -p 5000:5000 \
    -e REGISTRY_PROXY_REMOTEURL=https://registry-1.docker.io \
    --restart always \
    --name registry-docker.io registry:2

docker run -d -p 5001:5000 \
    -e REGISTRY_PROXY_REMOTEURL=https://registry.k8s.io \
    --restart always \
    --name registry-registry.k8s.io registry:2

docker run -d -p 5003:5000 \
    -e REGISTRY_PROXY_REMOTEURL=https://gcr.io \
    --restart always \
    --name registry-gcr.io registry:2

docker run -d -p 5004:5000 \
    -e REGISTRY_PROXY_REMOTEURL=https://ghcr.io \
    --restart always \
    --name registry-ghcr.io registry:2

Describe the solution you'd like

Should investigate this and see whether current restriction that caching proxy can only be set up for docker hub, and only globally, can be changed and provide more flexibility to configure caching proxies at workshop environment level of a workshop definition. This will depend on whether dind can be setup to use multiple caching proxies.

Describe alternatives you've considered

No response

Additional information

No response