Make config files readable for container user

This should be the default, but somehow doesn't work for some Docker
Compose versions?

Author: aequitas

docker/compose.yaml

@@ -714,8 +714,10 @@ services:
     configs:
       - source: prometheus_config
         target: /prometheus.yaml
+        mode: 0444
       - source: prometheus_rules_config
         target: /prometheus-rules.yaml
+        mode: 0444
 
     restart: unless-stopped
     logging:
@@ -746,6 +748,7 @@ services:
     configs:
       - source: alertmanager_config
         target: /alertmanager.yaml
+        mode: 0444
 
     restart: unless-stopped
     logging: