feat(content-docs): allow custom props through _category_.json

[taejs]

Motivation

Close #6690
Resolve Feature Request: allow-customizing-category-description-in-generated-index-cards

Have you read the Contributing Guidelines on pull requests?

yes. but I have no idea how to test it.

Test Plan

Related PRs

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[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🔴 Performance	48
🟢 Accessibility	100
🟢 Best practices	92
🟢 SEO	100
🟢 PWA	90

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[Josh-Cena]

Sorry, we don't want to add more root config fields for categories. Could you please just make categoryMetadata.customProps be passed to the final item? The idea is that the user can swizzle DocCard and implement whatever design through custom props.

[slorber]

Agree with @Josh-Cena : we want to enable users to bring their own customization abilities, not add just 2 new premade and unflexible attributes

[taejs]

Also agree. Thanks for the feedback. After addressing the review I'm trying to resolve this error.
The docs sidebar category metadata file path=${filePath} looks invalid

CustomProps are not acceptable even though I added sidebar validation.

[Josh-Cena]

CustomProps are not acceptable even though I added sidebar validation.

You added validation for the sidebar item, but not for the metadata file, which has another schema

[taejs]

Addressed reviews:
make categoryMetadata.customProps be passed to the final item.

[Josh-Cena]

Thanks, that looks great!