Add Loki recording rules and Grafana dashboard for tracking cache hit ratio, HTTP version and TLS version.

Please the commits for a bit more context. This is mainly because we are curious :)

The dashboard can be found here.

roles/loki/files/rules.yaml

@@ -4,3 +4,5 @@ groups:
     rules:
       - record: nginx:requests:rate1m
         expr: 'sum by (instance, server_protocol, ssl_protocol, ssl_cipher) (rate({job="nginx"}[1m] | json))'
+      - record: nginx:requests:rate1m
+        expr: 'sum by (instance, upstream_cache_status) (rate({job="nginx"}[1m] | json))'