conf: ajoute redis comme backend de cache

[LeSim]

est activé si la variable d'env REDIS_CACHE_URL est présente

[what-the-diff]

PR Summary

• Inclusion of Redis
  We've now added a software component called 'redis' to our project catalogue. This acts like a vault that stores precious data for faster data retrieval, hence improving our application's performance.

• Updated Settings in Production Environment
  We've also taught our application to switch its storage system to 'redis' when it's deployed in real-world settings and certain conditions are met. If this 'REDIS_CACHE_URL' element is present, the application will use 'redis' to store data, providing a better and speedier user experience.

[mfo]

p-e l'ajouter a env.example.optional