fix(filebeat): set explicit Docker-centric defaults

The default_config changed in elastic/beats@41ab08cd (v8.12.0) from
Docker to Kubernetes defaults. This change also changes the default
output from 'container' to 'input'.

Before we are able to update to v8.12, we need to set defaults which are
suitable for the configuration that docker-elk ships with.

Refs:
  https://github.com/elastic/beats/blob/v8.12.0/filebeat/autodiscover/builder/hints/config.go#L30-L51
  https://www.elastic.co/guide/en/beats/filebeat/8.12/filebeat-input-container.html
  https://www.elastic.co/guide/en/beats/filebeat/8.12/filebeat-input-filestream.html

extensions/filebeat/config/filebeat.yml

@@ -15,6 +15,10 @@ filebeat.autodiscover:
     # containers as they start and stop.
     - type: docker
       hints.enabled: true
+      hints.default_config:
+        type: container
+        paths:
+          - /var/lib/docker/containers/${data.container.id}/*-json.log
 
 processors:
   - add_cloud_metadata: ~