Handle CF Page build errors

[Carlgo11]

When the 2fa.directory build failed last week, the redirect script sent users in an infinite loop.
To stop this from happening again, I reworked the redirect script so that the logic now is the following:

1. If the user's origin region exists on the 2fa.directory, redirect to that region.
2. If 2fa.directory/int/ returns 200, redirect to /int/.
3. If all else fails, return the static page /503/. (HTTP 503 - Service Unavailable)
4. If the redirect script fails, return the static page /502/. (HTTP 502 - Bad Gateway)

I also created a 404 page and increased the caching ttl for existing regions.