chore: updated authelia docker-compose.yml

[xFuture603]

This pull request adds some improvements for the current example docker-compose.yml, configured with Authelia.

It adds:

• Valkey instead of Redis (even though this project does not resell Redis, Valkey is backed by the Linux Foundation and was essentially replaced via drop-in)
• adds password to the valkey configuration
• included a docker socket proxy to not bind the docker socket directly to Traefik (improves security if an attacker hijacks the Traefik instance via an exploit, for example)
• pin images to the currently latest available versions and their SHAs
• fixed some Authelia configuration warnings
• updated Traefik from v2 to v3 (currently latest available version)
• updated README.md

This PR complies with the DCO; https://developercertificate.org/