147 [deployment] Add Fluentd to docker environment.

[landerneRPi]

Add fluentd image, configuration in docker environment. Needs elasticsearch: next PR.

[Benvii]

Fluentd is actually useless if we don't feed it with our applications/containers logs (I don't think it's done automatically). In my understanding we need to use fluentd log driver for each containers.

See the documentation here : https://docs.fluentd.org/v/0.12/container-deployment/docker-compose#step-0-prepare-docker-compose.yml

This PR should be more complete :

• [ ] Include documentation about fluentd (update README to indicate that it's used, how to access it ...)
• [ ] Make at least 1 container to feed it so that it can be tested