feat: Clarify maintenance exclusion usage in no channel to release channel samples for GKE (terraform-google-modules#823)

Author: cslink

gke/standard/zonal/no-channel-to-release-channel/main.tf

@@ -65,7 +65,10 @@ resource "google_container_cluster" "no_upgrade" {
     }
     maintenance_exclusion {
       exclusion_name = "no_upgrades_exclusion"
-      start_time     = "2025-02-11T23:16:39Z"
+      # NOTE: Pick an interval for your exclusion with an end_time in the future
+      # otherwise the exclusion will have no effect.
+      # This example assumes that the exclusion is set on 2025-02-11.
+      start_time = "2025-02-11T23:16:39Z"
       # NO_UPGRADES exclusions are limited to 30 days.
       end_time = "2025-03-11T23:16:39Z"
       exclusion_options {
@@ -112,8 +115,11 @@ resource "google_container_cluster" "rc_regular" {
     }
     maintenance_exclusion {
       exclusion_name = "no_upgrades_exclusion"
-      start_time     = "2025-02-11T23:16:39Z"
-      end_time       = "2025-03-11T23:16:39Z"
+      # NOTE: Pick an interval for your exclusion with an end_time in the future
+      # otherwise the exclusion will have no effect.
+      # This example assumes that the exclusion is set on 2025-02-11.
+      start_time = "2025-02-11T23:16:39Z"
+      end_time   = "2025-03-11T23:16:39Z"
       exclusion_options {
         scope = "NO_UPGRADES"
       }
@@ -160,7 +166,10 @@ resource "google_container_cluster" "no_minor_or_node_upgrade" {
     }
     maintenance_exclusion {
       exclusion_name = "no_minor_or_node_upgrades_exclusion"
-      start_time     = "2025-02-11T23:16:39Z"
+      # NOTE: Pick an interval for your exclusion with an end_time in the future
+      # otherwise the exclusion will have no effect.
+      # This example assumes that the exclusion is set on 2025-02-11.
+      start_time = "2025-02-11T23:16:39Z"
       # This the end of standard support for 1.31.
       end_time = "2025-12-22T00:00:00Z"
       exclusion_options {