Initial release

This release brings up a Loki container (to be used as a remote Data Source by Grafana), as well as Grafana "promtail" instances on each Docker node to ingest container names and logs from all running containers into Loki. Promtail's configuration can be modified to ingest/relabel additional logs (such as system log files in /var/log/*) into Loki as well.

Promtail also has an API that can be exposed on port 9080 (not exposed externally by swarmstack/loki by default). Other logging facilities, such as Fluentd / Fluent Bit, can write directly to Loki.