docs: add loading="lazy" to iframes

[mattmaribojoc]

Related issue

Closes #

Scope of work

To further reduce the number of unnecessary requests per page, we can add loading="lazy" to our embedded iframe examples.

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Checklist

• Self code-reviewed
• Changes documented
• Semantic HTML
• SSR-friendly
• Caching friendly
• a11y for WCAG 2.0 AA
• examples created
• blocks created
• cypress tests created

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Latest commit: 9b5f1f6

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