feat(pgs): Configure cache-control, TTL, max body, exclude /check

[mac-chaffee]

• Increased the default TTL from 5 minutes to 10 minutes.
  • Reason: Sounds like the cache clearing has been working so we should be safe to raise it. 10 minutes is the default max-age for all Github Pages sites so it's probably a good standard to match.
• Made the default TTL configurable
• Set the default Cache-Control header to max-age: 600
  • Reason: Right now, the default value is set to the empty string, which is under-specified, but generally interpreted as if the header were missing. If the header is missing, browsers will still cache content on the client-side, but without an explicit TTL they will use a heuristic for calculating their own TTL (typically 10% of the time since the Last-Modified date). Explicitly setting the TTL is recommended instead of relying on that.
• Set the maximum cacheable body size.
  • In Implement caching using Souin (take 2) #159 I originally set this to 1MB but I was lazy and didn't want to add another config value so I just set it to the current max file size of 10MB :) Beware of RAM-based DDoS! May want to set a RAM limit on your pgs container in docker-compose.
• Excluded /check from caching.
  • Reason: Currently Souin is not caching /check anyway, but only because of UPSTREAM-ERROR-OR-EMPTY-RESPONSE, so I just made this more explicit.

PS: Thanks for the shout-out in the caching blog post!

[neurosnap]

LGTM! I'll add a RAM cap to pgs-web thanks for that call out.