use full image source and set version for all Chaosknoten compose images

Use a full image source and set and explicit version for all images in
Chaosknoten (docker-)compose files.
With Renovate now set up, it is feasible to explicitly set versions.

resources/chaosknoten/keycloak/docker_compose/compose.yaml.j2

@@ -46,7 +46,7 @@ services:
       - "8080:8080"
 
   db:
-    image: postgres:15.14
+    image: docker.io/library/postgres:15.14
     restart: unless-stopped
     networks:
       - keycloak