fix: Ignore RoutingError in New Relic error reporting (#14030)

Routing errors (404s) are expected in production and don't represent
actionable issues. Reporting them to New Relic creates noise and makes
it harder to spot real errors. Adds ActionController::RoutingError to
the New Relic error_collector.ignore_errors list so these are no longer
tracked as exceptions.

config/newrelic.yml

@@ -18,6 +18,9 @@ common: &default_settings
   distributed_tracing:
     enabled: true
 
+  error_collector:
+    ignore_errors: 'ActionController::RoutingError'
+
   # To disable the agent regardless of other settings, uncomment the following:
   agent_enabled: <%= ENV['NEW_RELIC_LICENSE_KEY'].present? && ENV.fetch('NEW_RELIC_AGENT_ENABLED', true)  %>