feat: :sparkles: Introduce light mode on the docs

[adevinwild]

Hey @kettanaito, I've reworked the light mode, as we had far too many conflicts, and I thought it was time to update it with everything that's been added and updated since then.

Don't hesitate to contact me if you'd like to reiterate any points!

Here is a quick video preview : https://streamable.com/mbj3li

And screenshots :

[!NOTE]
This PR follows this one : https://github.com/mswjs/mswjs.io/pull/278

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[adevinwild]

Added light theme for the code and pre elements, it's now a real light mode 🥳💡 :