better pointers to local registry hosting help

Repro steps:

1. Set up a k3d cluster on a remote machine with k3d cluster create --registry-create
2. Try to start tilt on a local machine

Result:

Build Failed: pushing image "localhost:44849/myservice": Get "http://localhost:44849/v2/": dial tcp [::1]:44849: connect: connection refused

The problem is that Tilt thinks the registry lives on localhost, but it lives on the remote machine. I think Tilt should do a better job pointing you to the right direction.

(registry auto-discovery is something that we collaborated with the k3d folks on. I think there might be things we can do on the tilt side to detect when you're connecting to a remote cluster with a local registry, but for now I think we can at least have a better error message)

Reproduce the reported setup with k3d cluster create --registry-create on a remote machine and Tilt on a local machine, then trace the registry auto-discovery and image-push failure path. Done means the failure explains that the registry resolves to the remote cluster rather than localhost and points users toward local registry hosting help.