This enables us to calculate the cache hit ratio, which may help
determine whether more caching would be beneficial.

Please note that this only counts requests for which caching is enabled
(e.g. {fastcgi,proxy}_cache is configured), e.g. for static served files
cache_status will be "".

[1] http://nginx.org/en/docs/http/ngx_http_upstream_module.html#var_upstream_cache_status

Mainly because we are curious. The data may also be used to decide if we
want to drop older versions of TLS.

The plan is to use this for creating metrics from the nginx log lines
(e.g. requests per second).

[1] https://grafana.com/docs/loki/latest/alert/#recording-rules