docker: switch to valkey

Recently-ish redis has switched to another license which isn't
open-source. An open-source fork named valkey has been established
under the Linux Foundation umbrella:
https://www.linuxfoundation.org/press/linux-foundation-launches-open-source-valkey-community

See also this LWN article:
https://lwn.net/Articles/966631/

valkey is a drop-in replacement for redis. Switch to valkey to
avoid depending on proprietary software.

docker-compose.yml

@@ -22,15 +22,15 @@ services:
       interval: 5s
 
   redis:
-    image: redis
+    image: valkey/valkey:alpine
     container_name: osrd-redis
     restart: unless-stopped
     ports: ["6379:6379"]
     volumes:
       - "redis_data:/data"
-    command: "redis-server --save 30 1 --loglevel warning"
+    command: "valkey-server --save 30 1 --loglevel warning"
     healthcheck:
-      test: ["CMD", "redis-cli", "ping"]
+      test: ["CMD", "valkey-cli", "ping"]
       start_period: 4s
       interval: 5s