Feat: Improve Nginx performance

From a review in another Nginx PR, there were some minor improvement comments:

1. Use Syntax: resolver address ... [valid=time] to shorten the valid attribute on the resolver to something like 5s as by default it'll use the default DNS TTL which might be large. In the backend for reverse proxy, you usually want to be reactive to change.
2. Shorten the default DNS timeout (30s, huge when requests are pending to be proxied) with a resolver_timeout to something like 5s.

This was attempted to be apart of the Nginx miration to cos-lib, but created PR smell. This should still be investigated.