Enable telegraf internal plugin everywhere

Change-Id: I95da01268aab720e454080a1965bf19e37ebf6ec
Related-PROD: PROD-30675
diff --git a/telegraf/agent/init.yml b/telegraf/agent/init.yml
index 64ef566..213d3ba 100644
--- a/telegraf/agent/init.yml
+++ b/telegraf/agent/init.yml
@@ -1,5 +1,6 @@
 classes:
 - service.telegraf.agent
+- system.telegraf.agent.input.internal
 - system.telegraf.agent.input.http_listener
 - system.telegraf.agent.output.prometheus_client
 - system.telegraf.sudo