Refactor post-build script that replaces relative and full URLs

When a stable version is built by single.Dockerfile, the normalize-links.sh script is used to replace the docs URLs to use a version.

It needs refactoring to be more quick and some bugs to be fixed.

• Remove old "symlink to CE" code !3702 (merged)
• Add support for macOS sed !3697 (merged)
• Replace multiple strings at once to make the script quicker !3701 (merged)
• Canonical URLs don't work on versioned docs !3677 (merged)