output ID of the api keys from usage_plan submodule (#30)

* chore: output api key id for usage_plan submodule

* chore: fix resource name

Author: hazmei

modules/usage_plan/outputs.tf

@@ -0,0 +1,6 @@
+output "api_keys_id" {
+  description = "ID of the api keys"
+  value = {
+    for k, v in aws_api_gateway_api_key.key : k => v.id
+  }
+}