feat(hydra): use keto-way of defining images

[aeneasr]

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• [ ] I have read the contributing guidelines and signed the CLA.
• [ ] I have referenced an issue containing the design document if my change introduces a new feature.
• [ ] I have read the security policy.
• [ ] I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security vulnerability, I confirm that I got green light (please contact [email protected]) from the maintainers to push the changes.
• [ ] I have added tests that prove my fix is effective or that my feature works.
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