feat: emit an event for karafka stats

This sends an event when Karafka emits a `statistics_emitted` event. It
can be toggled off with the following configuration:

```
karafka:
  insights:
    events: false
```

All metrics in the karafka plugin should now be disabled by default and
will need to be enabled by:
```
karafka:
  insights:
    metrics: true
```

(actually this was already the case, but I missed one metric, so now all metrics are disabled)

lib/honeybadger/karafka.rb

@@ -70,6 +70,10 @@ def initialize
       #
       # @param event [Karafka::Core::Monitoring::Event]
       def on_statistics_emitted(event)
+        if Honeybadger.config.load_plugin_insights_events?(:karafka)
+          Honeybadger.event("statistics_emitted.karafka", event.payload)
+        end
+
         return unless Honeybadger.config.load_plugin_insights_metrics?(:karafka)
 
         statistics = event[:statistics]
@@ -138,9 +142,7 @@ def on_error_occurred(event)
       def on_connection_listener_fetch_loop_received(event)
         time_taken = event[:time]
         messages_count = event[:messages_buffer].size
-
         consumer_group_id = event[:subscription_group].consumer_group.id
-
         extra_tags = { consumer_group: consumer_group_id }
 
         if Honeybadger.config.load_plugin_insights_metrics?(:karafka)
@@ -191,9 +193,10 @@ def on_consumer_consumed(event)
               #
               # @param event [Karafka::Core::Monitoring::Event]
               def on_consumer_#{after}(event)
-                tags = consumer_tags(event.payload[:caller])
-
-                increment_counter('consumer_#{name}', value: 1, **tags)
+                if Honeybadger.config.load_plugin_insights_metrics?(:karafka)
+                  tags = consumer_tags(event.payload[:caller])
+                  increment_counter('consumer_#{name}', value: 1, **tags)
+                end
               end
         RUBY
       end