Update grafana/promtail Docker tag to v3

Author: renovate[bot]

deployment/advanced/docker-compose/docker-compose.yml

@@ -19,7 +19,7 @@ services:
             - loki
 
     promtail:
-        image: grafana/promtail:2.9.6
+        image: grafana/promtail:3.4.2
         volumes:
             - './configs/:/var/log'
         command: -config.file=/etc/promtail/config.yml