Send agents' structured logs into ELK for visualization

[Ullaakut]

Instead of using the standard output for visualizing the metrics, using an appropriate solution such as Kibana or Greylog would be much more elegant. It would allow for users to customize a dashboard depending on their needs, to create graphs, to configure their alarms using a GUI instead of environment variables or command line arguments, etc.

The current logger is already able to send structured logs as JSON to a Logstash/Elastic instance.

• Add configuration variable to determine whether or not the Agent is plugged into ELK
• If it is, instantiate the logger in the non-pretty mode (outputs JSON)
• Add docker-compose.yml file and a docker-compose.override.yml file that contains a configuration that allows switching from stdout to an output through a log driver into Logstash or ElasticSearch