L2SS-970: add loki docker-compose file

docker-compose/loki.yml

+#
+# Docker compose file that launches a LOKI instance.
+# See https://grafana.com/docs/loki/latest/installation/docker/
+#
+#
+
+version: "3"
+
+services:
+  loki:
+    image: grafana/loki:2.6.0
+    container_name: ${CONTAINER_NAME_PREFIX}loki
+    logging:
+      driver: "json-file"
+      options:
+        max-size: "100m"
+        max-file: "10"
+    networks:
+      - control
+    ports:
+      - "3100:3100"
+    command: -config.file=/etc/loki/local-config.yaml
+
+  promtail:
+    image: grafana/promtail:2.6.0
+    container_name: ${CONTAINER_NAME_PREFIX}promtail
+    logging:
+      driver: "json-file"
+      options:
+        max-size: "100m"
+        max-file: "10"
+    volumes:
+      - /var/log:/var/log
+    command: -config.file=/etc/promtail/config.yml
+    networks:
+      - control