feat(plugin-docs): docs sidebar item link: support "autoAddBaseUrl" attribute

[slorber]

Motivation

See #7839 (comment)

We automatically add site baseUrl to links by default, including external links (those using the pathname:/// protocol).

But sometimes it doesn't make sense to apply that baseUrl. For example, if you have an i18n site but want to link to a local HTML file that is not localized, you don't want the /locale/ baseUrl to be applied.

We already have an autoAddBaseUrl: false escape hatch in props <Link>, but it's not possible to use this prop through the sidebar

Note: autoAddBaseUrl remains undocumented for now but we mention it in issues. Maybe it's not the good API we want to keep. Maybe we should autoAddBaseUrl by default if the baseUrl is an i18n baseUrl 🤷‍♂️ For now I just expose the already existing hidden prop to provide the escape hatch, but we'll have to clean up the Docusaurus Link component at some point and expose a properly documented APIs.

Test Plan

preview + dogfooding

Test links

https://deploy-preview-7949--docusaurus-2.netlify.app/tests/docs

(unfortunately, we don't deploy FR anymore to deploy previews => not really possible to test, but it works fine locally)

[netlify]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 79	🟢 98	🟢 100	🟢 100	🟠 80	Report
/docs/installation	🟠 74	🟢 100	🟢 100	🟢 100	🟢 90	Report

[github-actions]

Size Change: 0 B

Total Size: 812 kB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	52.5 kB
website/build/assets/css/styles.********.css	111 kB
website/build/assets/js/main.********.js	608 kB
website/build/index.html	40.7 kB

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