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: instance_http_version_tls_version_tls_cipher:requests:rate1m
         expr: 'sum by (instance, http_version, tls_version, tls_cipher) (rate({job="nginx"}[1m] | json http_version="server_protocol", tls_version="ssl_protocol", tls_cipher="ssl_cipher"))'
+      - record: instance_cache_status:requests:rate1m
+        expr: 'sum by (instance, cache_status) (rate({job="nginx"}[1m] | json cache_status="upstream_cache_status"))'