Update configure-controllers.mdx (#3407)

Not correct based on: 
https://developer.hashicorp.com/boundary/docs/configuration/controller#public_cluster_addr

website/content/docs/install-boundary/configure-controllers.mdx

@@ -171,7 +171,7 @@ controller {
 
   # This is the public hostname or IP where the workers can reach the
   # controller. This should typically be a load balancer address
-  public_cluster_address = "example-cluster-lb.example.com"
+  public_cluster_addr = "example-cluster-lb.example.com"
 
   # Enterprise license file, can also be the raw value or env:// value
   license = "file:///path/to/license/file.hclic"