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/pretalx/docker_compose/compose.yaml.j2

@@ -15,7 +15,7 @@ services:
       - pretalx_net
 
   redis:
-    image: redis:latest
+    image: docker.io/library/redis:8.2.2
     restart: unless-stopped
     volumes:
       - redis:/data
@@ -23,7 +23,7 @@ services:
       - pretalx_net
 
   static:
-    image: docker.io/library/nginx
+    image: docker.io/library/nginx:1.29.2
     restart: unless-stopped
     volumes:
       - public:/usr/share/nginx/html
@@ -33,7 +33,7 @@ services:
       - pretalx_net
 
   pretalx:
-    image: pretalx/standalone:latest
+    image: docker.io/pretalx/standalone:v2025.1.0
     entrypoint: gunicorn
     command:
       - "pretalx.wsgi"
@@ -78,7 +78,7 @@ services:
       - pretalx_net
 
   celery:
-    image: pretalx/standalone:latest
+    image: docker.io/pretalx/standalone:v2025.1.0
     command:
       - taskworker
     restart: unless-stopped