docs: add custom image extractor example for ImageValidatingPolicy

[Pittu-Sharma]

Related issue

Fixes #1915

Proposed Changes

This PR addresses the documentation gap identified in issue #1915 by adding a comprehensive and functional example of an ImageValidatingPolicy that utilizes the custom image extractor field (spec.images).

Key changes:

• Added a new Custom Image Extractor section to the ImageValidatingPolicy documentation.
• Provided a logically complete YAML example demonstrating how to extract images from a custom resource (example.io/v1/myresources) and perform subsequent signature verification.
• Expanded existing YAML snippets throughout the document to be logically complete policies (removing partial # ... patches) to improve documentation quality and ensure examples are copy-paste ready.

Checklist

• I have read the contributing guidelines.
• I have inspected the website preview for accuracy.
• I have signed off my issue (using git commit -s).

[Pittu-Sharma]

Hi @JimBugwadia, I have completed the documentation for issue #1915. I've added a functional example for the custom image extractor (spec.images) and also took the opportunity to expand the existing YAML snippets in the file into logically complete policies to improve the documentation's utility.

I have verified the changes locally using npm run dev and ensured the build and link checks pass. Please let me know if any further refinements are needed. Thanks!

[Suhani95]

Hey @Pittu-Sharma , I noticed this PR includes several changes outside the documentation scope:

• Hostname matching updates in src/utils/versions.ts
• Plugin/integration changes in astro.config.mjs

Could we split the programmatic/config/dependency changes into a separate PR and keep this one focused on the .mdx documentation updates?

[Suhani95]

could we add a small sample custom resource object near the example to show what object.foo.bar maps to? That would make the CEL extraction path easier to understand for users working with CRDs.

[Pittu-Sharma]

Hi @Suhani95,

Thank you for the review and the suggestions! I've updated the PR to address both of your points:

1. Focused Scope: I've removed the programmatic and configuration changes (src/utils/versions.ts, astro.config.mjs, and the dependency lockfiles) from this branch so that this PR is now strictly focused on the .mdx documentation updates. I'll be opening a separate PR for those other updates.
2. Custom Resource Example: I've added a small sample custom resource YAML snippet right before the custom image extractor policy example. This clearly demonstrates what the object.foo.bar CEL expression maps to, which should make it much easier for users working with CRDs to understand the extraction path.

Please let me know if anything else needs adjusting!