fix(seo): docs breadcrumb structured data should use JSON-LD and filter unliked categories

[johnnyreilly]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes The structured data items may contain fields that do not comply with Google's guidelines, which can negatively impact SEO. #9319) and the maintainers have approved on my working plan.

There seem to be some failing tests, but as far as I can tell these are not related to my changes.

Motivation

To have the structured data approach favoured by Google (JSON-LD) and also consistency.

Test Plan

Test links

Deploy preview: https://deploy-preview-10888--docusaurus-2.netlify.app/docs/configuration/

Related issues/PRs

#9319

[netlify]

✅ [V2]

Name	Link
🔨 Latest commit	428988d
🔍 Latest deploy log	https://app.netlify.com/sites/docusaurus-2/deploys/67a64816c6e7790008e87ac5
😎 Deploy Preview	https://deploy-preview-10888--docusaurus-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	Report
/	🟠 70	🟢 98	🟢 96	🟢 100	Report
/docs/installation	🟠 53	🟢 97	🟢 100	🟢 100	Report
/docs/category/getting-started	🟠 71	🟢 100	🟢 100	🟠 86	Report
/blog	🟠 62	🟢 96	🟢 100	🟠 86	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 65	🟢 92	🟢 100	🟢 100	Report
/blog/tags/release	🟠 64	🟢 96	🟢 100	🟠 86	Report
/blog/tags	🟠 74	🟢 100	🟢 100	🟠 86	Report

[slorber]

As explained here: #9319 (comment)

I consider this PR a valid change

It is able to pass validations on both tools for breadcrumbs with/without unlinked categories

• https://deploy-preview-10888--docusaurus-2.netlify.app/docs/markdown-features/head-metadata/

• https://validator.schema.org/#url=https%3A%2F%2Fdeploy-preview-10888--docusaurus-2.netlify.app%2Fdocs%2Fmarkdown-features%2Fhead-metadata%2F

• https://deploy-preview-10888--docusaurus-2.netlify.app/docs/migration/v2/

• https://validator.schema.org/#url=https%3A%2F%2Fdeploy-preview-10888--docusaurus-2.netlify.app%2Fdocs%2Fmigration%2Fv2%2F

• https://search.google.com/test/rich-results/result?id=wiKGqWaEZ0hrj-NWZ77Rvw

---

I would have preferred if unlinked categories appeared in the breadcrumb, but since an URL is required and no fallback option seems good, I think this change is fine 👍