Feat: integrate registry proxy in k3d

[iwilltry42]

Original issue comment below:

I ran into this issue as well (came up because I kept hitting docker.io rate limits), so created a custom registry that proxies all image requests to the host docker instance: https://github.com/ligfx/k3d-registry-dockerd

I use it like so:

configfile=$(mktemp)
cat << HERE > "$configfile"
apiVersion: k3d.io/v1alpha5
kind: Simple
registries:
  create:
    image: ligfx/k3d-registry-dockerd:v0.1
    proxy:
      remoteURL: "*"
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
HERE
k3d cluster create mytest --config "$configfile"

It's also had the side effect of significantly speeding up cluster creation and pod rollout, which is nice!

Originally posted by @ligfx in #19 (comment)

[iwilltry42]

@ligfx if you're up for it, we could move your repo over to the k3d-io org or even integrate it into the k3d repo (just like proxy and lb).
Then we add the builds to the official CI pipeline.

Feature wise I would add a flag to cluster create that will use your registry.
Same for registry create.
So just shortcuts to what you'd else do manually.

I'd assign you as the code owner of that part, no matter where it lands.

WDYT?