Added backtrace to custom exception (#4)

Author: amoludage

lib/datadog_notifier.rb

@@ -3,10 +3,14 @@
 require 'ddtrace'
 require 'datadog_notifier_exception'
 
+# DatadogNotifier for custom error notification to datadog
 class DatadogNotifier
   def self.notify(exception, payload = {})
     root_span = find_root_span(Datadog::Tracing.active_span)
-    exception = DatadogNotifierException.new exception if exception.is_a?(String)
+    if exception.is_a?(String)
+      exception = DatadogNotifierException.new exception
+      exception.set_backtrace(payload.inspect)
+    end
     root_span.set_error(exception)
     root_span.set_tag('custom_dd_notifier', true)
     root_span.set_tag('payload', payload.to_json) if payload.present?