peristent volumes for docker-compose

[StefanSa]

@qclaogui
it would be very helpful for docker-compose to set up persistent volumes for minio S3 and Grafana.
The path of the volumes could be published in .env.
It is important to know, that by default the Grafana container will run with uid/gid 472, so you can chown -R 472:472 /your/grafana/dir on the host, then the container will be able to write to it.