404 page added

[jtmst]

Description

Relates to #14711

• Adds the 404 page component
• Adds the common and popular component
• Modifies the getGlobalElements call to allow for only headerData calls
• Adds unit tests for 404 page

Testing done

Local visual testing

Screenshots

QA steps

Navigate to any non-existant page
Verify that 404 page matches prod

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[tjheffner]

I think I would restructure this to match [[...slug]].tsx a little closer, unless there's a specific reason that the 404 page needs handled in this way.

const { headerFooterData } = await getGlobalElements() feels a bit cleaner than the let & try catch block. slug has the whole getStaticProps function in a try catch