Alternate fix to #36221.
This doesn't address every issue, but it fixes the broken links for Home and Examples. This also fixes the 404 for the utilities/opacity/ page. What remains is figuring out what to do about two situations:
- Disabled links for components added in later releases (e.g., https://twbs-bootstrap.netlify.app/docs/5.1/components/placeholders/)
- Providing a general "v5.1 docs link" instead of a page-specific link
TBD on both those.
/cc @julien-deramond