fix: update observability stack versions for security fixes

- Prometheus: v2.48.0 → v2.55.1 (fixes docker/crypto vulnerabilities)
- Grafana: 10.2.2 → 11.4.0 (addresses CVEs in older version)
- Loki: 2.9.3 → 3.3.2 (security patches)
- cAdvisor: v0.47.2 → v0.51.0 (updated dependencies)
- Redis Exporter: v1.55.0 → v1.67.0 (latest stable)

Author: NormB

.env.example

@@ -25,12 +25,12 @@ PGBOUNCER_VERSION=latest
 FORGEJO_VERSION=1.21.11-0
 
 # Observability Stack:
-PROMETHEUS_VERSION=v2.48.0
-GRAFANA_VERSION=10.2.2
-LOKI_VERSION=2.9.3
+PROMETHEUS_VERSION=v2.55.1
+GRAFANA_VERSION=11.4.0
+LOKI_VERSION=3.3.2
 VECTOR_VERSION=0.50.0-debian
-CADVISOR_VERSION=v0.47.2
-REDIS_EXPORTER_VERSION=v1.55.0
+CADVISOR_VERSION=v0.51.0
+REDIS_EXPORTER_VERSION=v1.67.0
 
 # ===========================================================================
 # HashiCorp Vault Configuration (Secrets Management & PKI)