* perf: no longer generate unnecessary nginx conf for better performance.
* benchmark: sync nginx.conf for fake-apisix.
> Is this PR backward compatible?
Disable two plugins by default(proxy-cache, proxy-mirror), if the user wants to enable them, need to modify the conf/config.yaml by manual.
* optimize: Use lru to avoid resolving IP addresses repeatedly .
Cached the global rules to `ctx` .
* optimzie: used a longer time interval for etcd and flush access log.
* optimize: return upstream node directly if the count is 1 .
* optimize: avoid to cache useless variable.
