feat: add new ssg.strict config

[chenjiahan]

Summary

Add a new ssg.strict config.

export default {
  ssg: {
    strict: true,
  },
};

Related Issue

See #1317 for more background.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

✅ Deploy Preview for aquamarine-blini-95325f ready!

Name	Link
🔨 Latest commit	5476689
🔍 Latest deploy log	https://app.netlify.com/sites/aquamarine-blini-95325f/deploys/66bc29789fd83d000820017b
😎 Deploy Preview	https://deploy-preview-1325--aquamarine-blini-95325f.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 63 (🔴 down 17 from production) Accessibility: 97 (no change from production) Best Practices: 92 (no change from production) SEO: 92 (no change from production) PWA: - View the detailed breakdown and full score reports

---

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

[zoolsher]

LGTM