feat(shortcodes): add lazy-loading YouTube embed

[abdalrahmanshaban0]

What does this PR change? What problem does it solve?

Adds a new shortcode for embedding YouTube videos with:

• loading="lazy" for performance
• youtube-nocookie.com for privacy
• customizable title for accessibility

Example on how to use it:
{{< youtube_lazy VID_ID "TITLE">}}

This improves page speed and ensures more privacy-friendly video embeds.

Was the change discussed in an issue or in the Discussions before?

No

PR Checklist

• This change adds/updates translations and I have used the template present here.
• I have enabled maintainer edits for this PR.
• I have verified that the code works as described/as intended.
• This change adds a Social Icon which has a permissive license to use it.
• This change does not include any CDN resources/links.
• This change does not include any unrelated scripts such as bash and python scripts.
• This change updates the overridden internal templates from HUGO's repository.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud