feat: properly localize the 404 page including meta tags

[ramboz]

The content for the 404 page is already properly localized through #371, but the meta tags still need to be adjusted:

Test URLs:

• Before: https://main--petplace--hlxsites.hlx.page/invalid
• After:
  • https://localized-404--petplace--hlxsites.hlx.live/invalid
  • https://localized-404--petplace--hlxsites.hlx.live/invalid?martech=off
  • https://localized-404--petplace--hlxsites.hlx.page/en-gb/invalid
  • https://localized-404--petplace--hlxsites.hlx.page/en-gb/invalid?martech=off

[aem-code-sync]

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Commits

• 801d21a ✅ (latest)

[aem-code-sync]

Page	Scores	Audits	Google
/invalid		Lighthouse returned error: ERRORED_DOCUMENT_REQUEST. Lighthouse was unable to reliably load the page you requested. Make sure you are testing the correct URL and that the server is properly responding to all requests. (Status code: 404)
/invalid?martech=off		Lighthouse returned error: ERRORED_DOCUMENT_REQUEST. Lighthouse was unable to reliably load the page you requested. Make sure you are testing the correct URL and that the server is properly responding to all requests. (Status code: 404)
/en-gb/invalid		Lighthouse returned error: ERRORED_DOCUMENT_REQUEST. Lighthouse was unable to reliably load the page you requested. Make sure you are testing the correct URL and that the server is properly responding to all requests. (Status code: 404)
/en-gb/invalid?martech=off		Lighthouse returned error: ERRORED_DOCUMENT_REQUEST. Lighthouse was unable to reliably load the page you requested. Make sure you are testing the correct URL and that the server is properly responding to all requests. (Status code: 404)