Implement `loadimage` addon for GKE

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Problem Statement

When running tests against GKE, it would be handy if the `loadimage.Addon` could handle pushing images to Artifact Repository to make them available from the cluster.

### Proposed Solution

- Extend the `loadimage.Addon` implementation to handle GKE cluster type (possibly by pushing the image to Artifact Repository)
- Add E2E test verifying that a locally built image after loading it with the addon is available from a GKE cluster

### Additional information

_No response_

### Acceptance Criteria

- [ ] When `loadimage.Addon` is deployed with a locally built image, the image is available from a GKE cluster in the same Google Cloud project

Locate the loadimage.Addon implementation and its existing cluster-type handling, then review the project’s E2E test setup. Implement support for a locally built image on GKE and add the requested E2E coverage; done means the image is available from a GKE cluster in the same Google Cloud project.

Written by the indexing model from the issue text.