Configuration hot reload

In Kubernetes, ConfigMaps, Secrets and similar are "hot swapped" when updated (as long as they are mounted properly).

Since our application is mostly stateless, we could make use of this to hot reload the configuration, or at least the part that makes sense (such as the group configs), without restarting the entire pod. This would allow for 0 downtime updates to configuration even with a single pod instance.

One may find inspiration in the ArcSwap implementation in the RustlsConfig struct used for reloading the certificates.

Suggestion: separate "server config" and "groups config". Server config cannot be reloaded, while group config SHOULD be reloaded.