[TASK] Add Dependabot for automated dependency updates #818

Certification

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

Description

See https://github.com/kubeflow/model-registry/blob/main/.github/dependabot.yml for reference.

Acceptance Criteria

• Create .github/dependabot.yml
• Group mod-arch-* packages together in a single PR to keep these packages up to date
• Should also monitor: Go modules (backend & controller), npm packages (frontend), Docker images, GitHub Actions