feat: implement horizontal scaling optimizations for authz service

- Add /health and /ready endpoints for load balancer health checks
- Replace in-memory JWT token cache with Redis for multi-replica support
- Reduce DB connection pool from 100 to 25 connections per replica
- Add distributed rate limiting (100 req/min + 20 burst) using Redis
- Implement circuit breakers for DB and Redis to prevent cascading failures

This enables the service to scale horizontally with multiple replicas
behind a load balancer without exhausting database connections or
maintaining separate token caches per instance.

models/health.go

@@ -0,0 +1,7 @@
+package models
+
+// HealthResponse represents the health check response
+type HealthResponse struct {
+	Status   string            `json:"status"`
+	Services map[string]string `json:"services,omitempty"`
+}

models/rate_limiter.go

@@ -0,0 +1,7 @@
+package models
+
+// RateLimitConfig holds rate limiting configuration
+type RateLimitConfig struct {
+	RequestsPerMinute int
+	BurstSize         int
+}