Proper design for HTTP 4xx/5xx pages

We should have a html page that we can use in the web server config for e.g. HTTP 404 and 502 or 503 errors that looks in line with the other postmarketos.org pages.

So I guess in the end there should be e.g. 404.html and 503.html in the web server root. Web server configuration will be done by the infra team in the end, not in scope of this issue.

The 5xx page(s) should link to status.postmarketos.org, something like "Please check status.postmarketos.org" with some more nice text.

I'd be thinking of something like this.