docs(website): added checkbox to toggle linter in playground

[PatrM]

Summary

Fixes #3010

I added a checkbox in the Linter section.

• The Linter / Diagnostics tab in Playground now displays the message Linter is currently disabled, in case the tab is open, but the checkbox unchecked
• The nursery rules checkbox becomes disabled, but displays its previous value if linting is disabled

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[sebmck]

Thank you so much!