feat: expose security group ID for ElastiCache Redis cluster (#43)

* feat: expose security group ID for ElastiCache Redis cluster

- Add security_group_id output to expose the security group ID from the underlying ElastiCache Redis module
- This enables proper configuration of inbound and outbound traffic rules for ECS services

* Update src/outputs.tf

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: milldr

src/outputs.tf

@@ -2,3 +2,8 @@ output "redis_clusters" {
   description = "Redis cluster objects"
   value       = local.enabled ? local.clusters : {}
 }
+
+output "security_group_id" {
+  description = "The security group ID of the ElastiCache Redis cluster"
+  value       = local.enabled ? try(module.redis_clusters[keys(var.redis_clusters)[0]].security_group_id, null) : null
+}