Increase custom_insights_events.max_samples_stored

The previous default value was 1000. The new default is 3000.

This new number is based on  OATS results from multiple language agents

lib/new_relic/agent/configuration/default_source.rb

@@ -2004,7 +2004,7 @@ def self.enforce_fallback(allowed_values: nil, fallback: nil)
           :description => 'If `true`, the agent captures [custom events](/docs/insights/new-relic-insights/adding-querying-data/inserting-custom-events-new-relic-apm-agents).'
         },
         :'custom_insights_events.max_samples_stored' => {
-          :default => 1000,
+          :default => 3000,
           :public => true,
           :type => Integer,
           :allowed_from_server => true,