Configuring of points per UDP packet

This allows users to configure the number of points stored in a single
UDP packet. This in turn can be used to reduce the number of UDP packets
being sent at the cost of these packets being somewhat larger.

The default setting is 1 point per packet so nothing changes for
existing users.

lib/gitlab/metrics.rb

@@ -14,7 +14,8 @@ module Gitlab
         method_call_threshold: current_application_settings[:metrics_method_call_threshold],
         host:                  current_application_settings[:metrics_host],
         port:                  current_application_settings[:metrics_port],
-        sample_interval:       current_application_settings[:metrics_sample_interval] || 15
+        sample_interval:       current_application_settings[:metrics_sample_interval] || 15,
+        packet_size:           current_application_settings[:metrics_packet_size] || 1
       }
     end
 
@@ -41,9 +42,9 @@ module Gitlab
       prepared = prepare_metrics(metrics)
 
       pool.with do |connection|
-        prepared.each do |metric|
+        prepared.each_slice(settings[:packet_size]) do |slice|
           begin
-            connection.write_points([metric])
+            connection.write_points(slice)
           rescue StandardError
           end
         end