Using env variable to detect Netlify deployment

[diemol]

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Description

Adding env var to detect netlify deployments

Motivation and Context

It will allow to preview PRs by deploying them to Netlify

Types of changes

• Change to the site (I am attaching a screenshot showing the before and after)
• Code example added (and I also added the example to all translated languages)
• Improved translation
• Added new translation (and I also added a notice to each document missing translation)

Checklist

• I have read the contributing document.
• I have used hugo to render the site/docs locally and I am sure it works.