new-feature: Add custom 404 page to our website

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We are working on a new website.

We should add a custom 404 page. That's more helpful then the default implementation.

Comment below from Hugo

Generate the project locally and then simply copy the 404.html from the language directory under /static/.

The staticDir lives outside Hugo’s Multilingual Mode, therefore a 404.html under the root of /static/ will be served under the root of the domain without having to use any shell command during deployment.