[EPIC] Workspace Redirects + Lifecycle

### Certification

- [x] I certify I am an Epic Owner for Kubeflow Notebooks 2.0 and expected to create planning-related issues.

### User Story

As an ML Platform Admin, Joel needs the ability to define container images that can replace older versions of the same image. He requires a mechanism to signify that a given Workspace using an older container image should, at the earliest convenience, be updated and restarted to leverage a newer image. This is crucial for pushing updates to dependencies to tap into the latest features, deprecating libraries not actively in use, or responding to security vulnerabilities.

As an AI/ML practitioner, Bella needs to be informed when the container image for her active workspace has a newer, preferred image available. She wants to understand the details of the new image, including what is changing, so she can decide when to apply the update. This allows her to control the timing of updates to avoid disrupting her ongoing work while still leveraging the latest features, security fixes, and dependency updates.

No files, tests, or entry points are identified. Start by reviewing the user stories and clarifying the expected workspace redirect and lifecycle behavior with the project maintainers. Done requires an agreed implementation scope and acceptance criteria for image replacement, update notification, and restart timing.

Written by the indexing model from the issue text.