Add GKE Stackdriver Monitoring changes to upgrade guide (#4683)
Add GKE Stackdriver Monitoring changes to upgrade guide (#4683)

Signed-off-by: Modular Magician <86ce7da8ad74b1c583667a2bebd347455fa06219@google.com>
hashicorp/terraform-provider-google,terraform-providers/terraform-provider-google,hashicorp/terraform-provider-google,terraform-providers/terraform-provider-google,terraform-providers/terraform-provider-google,hashicorp/terraform-provider-google,hashicorp/terraform-provider-google,terraform-providers/terraform-provider-google,terraform-providers/terraform-provider-google