ci: add check for policy samples

[sprt]

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

This adds a GitHub Action workflow to check that the policy samples have
been updated with each PR. We'll add it as a required check to catch
policy errors earlier in the dev process.

I also tweaked the update script to have better error handling, and I
simplified the PR template to make it more readable.

[Redent0r]

This looks great to me @sprt, thank you!

I did noticed the check is not showing as required yet

Not sure if it'll change to required once it's merged

[sprt]

@Redent0r Will add it as required when we merge it!