implement a 410 Gone page

[lonnen]

Description

When we decommission mozilla projects we sometimes want to retain the domain name for some time to prevent squatting or malicious syphoning. It would be useful to have a single HTTP 410 Gone error page to point these towards, like our 404 and 500 error pages. This would be less confusing for users than a 404, and provide an opportunity to engage with them in a moment of possible surprise or frustration.

Existing 410 pages like https://www.mozilla.org/projects/user-docs/local/ partially implement this, but has no explanatory text that the resource is gone.

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💛 Success Criteria 💛

• an official looking page is returned explaining the page you were seeking is gone
• the server http response code is 410 so that caching can appropriately handle future requests

❗ Risks ❗

• having a generic page may not provide enough context to a surprised user

Tasks

• note from reporter: I don't know enough to break this down into useful subtasks

[lonnen]

my example use cases are all microsites we made for demos or initiatives that have passed their moment, like https://inhumanads.com/ or https://games.mozilla.org/