Set `X-Date-Temporal-Context: [past|present|future]` header for easy cache rules:
- Cache `past` things heavily
- Cache `present`/`future` things for 5 minutes
This accomplishes the goal we set out for:
> - We can cache all responses except for the latest UTC day (and anything in the future). ex. `/!aMzLHLvScQCGKDNqCB:gitter.im/date/2022/10/13`
> - For the latest day, we could set the cache expire after 5 minutes or so
>
> *-- [Matrix Public Archive deployment issue](https://github.com/vector-im/sre-internal/issues/2079)*
And this way we don't have to do any fancy date parsing and comparison from the URL which is probably not even possible Cloudflare cache rules.