Change filebeat.config.modules.enabled to true

As per https://www.elastic.co/guide/en/beats/filebeat/current/filebeat-configuration-reloading.html#load-module-config, the default value of filebeat.config.modules.enabled is `true`. Having it as `false` in filebeat.reference.yml would bring in confusion.

filebeat/filebeat.reference.yml

@@ -1024,7 +1024,7 @@ filebeat.inputs:
  #reload.enabled: true
  #reload.period: 10s
  #modules:
- #enabled: false
+ #enabled: true
  #path: modules.d/*.yml
  #reload.enabled: true
  #reload.period: 10s