genpolicy: add support for PodDisruptionBudget spec

[arc9693]

Merge Checklist

• Followed patch format from upstream recommendation: https://github.com/kata-containers/community/blob/main/CONTRIBUTING.md#patch-format
  • Included a single commit in a given PR - at least unless there are related commits and each makes sense as a change on its own.
• Aware about the PR to be merged using "create a merge commit" rather than "squash and merge" (or similar)
• genPolicy only: Ensured the tool still builds on Windows
• genPolicy only: Updated sample YAMLs' policy annotations, if applicable
• The upstream-missing label (or upstream-not-needed) has been set on the PR.

Summary

Modified yaml.rs to prevent panic when genpolicy is called for a PodDisruptionBudget spec.

Associated issues

https://microsoft.visualstudio.com/OS/_workitems/edit/48139280/

Links to CVEs

Test Methodology

Pipeline e2e tests: https://dev.azure.com/mariner-org/mariner/_build/results?buildId=493910&view=results
Local test:
Spec:

Before:

After: