feat: onBrokenMarkdownAssets config option to catch bad asset paths without failing

[Josh-Cena]

Motivation

Resolve #3992. This config option is used for both links and images as they are treated in pretty much the same fashion.

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

TODO

[netlify]

✔️ [V2]

🔨 Explore the source changes: 2f45d8b

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/61f3b28e64a4160008b6431c

😎 Browse the preview: https://deploy-preview-5909--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	71
🟢 Accessibility	100
🟢 Best practices	93
🟢 SEO	100
🟢 PWA	92

Lighthouse ran on https://deploy-preview-5909--docusaurus-2.netlify.app/

[github-actions]

Size Change: +31 B (0%)

Total Size: 755 kB

Filename	Size	Change
website/build/assets/js/main.********.js	573 kB	+31 B (0%)

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	47 kB
website/build/assets/css/styles.********.css	105 kB
website/build/index.html	30.1 kB

_{compressed-size-action}

[Josh-Cena]

Not sure what should happen if the path doesn't exist though: should it still be require? Or should it stay as-is?

[slorber]

Not sure what should happen if the path doesn't exist though: should it still be require? Or should it stay as-is?

If you convert it to require and it doesn't exist, it will fail the build anyway so using anything other than 'throw' will lead to log + error.

Not sure how to easily test for this without a site fixture or E2E test

[Josh-Cena]

Closing. To be resolved after #6370