Updated nuxt integration tutorial

[adrianwix]

I updated it to explain how to register the env variables. This is the only thing that took me some time since I forgot the to use env variables in the client side they must be registered in nuxt.config (plus the plugin only work client side)

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• [ ] Titles are in sentence case
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🔨 Latest commit	2d76232c2d9a092a7dd55e78d466dfe669e3f31c

[joethreepwood]

@ivanagas Adding you so you can either get this over the line, or close. Whichever you think best.

[ivanagas]

Now overtaken by #5919