fix: Outputs for pool need to account for complexity (philips-labs#1970)

* fix: outputs for pool need to account for complexity

As the pool is optional the output needs to take this into account and access the first instance in the list. We also must output null if not set.

* Ensure pool role is output from main module

modules/runners/outputs.tf

@@ -23,5 +23,5 @@ output "role_scale_down" {
 }
 
 output "role_pool" {
-  value = length(var.pool_config) == 0 ? {} : module.pool.role_pool
+  value = length(var.pool_config) == 0 ? null : module.pool[0].role_pool
 }

outputs.tf

@@ -9,6 +9,7 @@ output "runners" {
     role_runner             = module.runners.role_runner
     role_scale_up           = module.runners.role_scale_up
     role_scale_down         = module.runners.role_scale_down
+    role_pool               = module.runners.role_pool
   }
 }