Pull sandbox from private registry

[sigurdfalk]

Problem Statement

We want to create a custom sandbox and only have an auth protected registry available. Would be nice to be able to pull sandboxes using custom image credentials

Proposed Design

Props for image credentials on the sandbox start command

Alternatives Considered

Building the image locally, but we are currently restricted by image size limits causing the start command to fail

Agent Investigation

No response

Checklist

• I've reviewed existing issues and the architecture docs
• This is a design proposal, not a "please build this" request