fix: mark outputs as sensitive

[jvelasquez]

Using the latest 5.0.0 + terragrunt, I have run into the following errors:

### shortened for clarity 
azurerm_kubernetes_cluster.main: Creation complete after 11m7s [id=/subscriptions/xxxx/resourceGroups/resource-group/providers/Microsoft.ContainerService/managedClusters/yyyy]

│ Error: Output refers to sensitive values
│   on outputs.tf line 11:
│   11: output "admin_client_certificate" {
│   16: output "admin_client_key" {
│   21: output "admin_cluster_ca_certificate" {
│   26: output "admin_host" {
│   31: output "admin_password" {
│   36: output "admin_username" {
 
│ To reduce the risk of accidentally exporting sensitive data that was
│ intended to be only internal, Terraform requires that any root module
│ output containing sensitive data be explicitly marked as sensitive, to
│ confirm your intent.
│ 
│ If you do intend to export this data, annotate the output value as
│ sensitive by adding the following argument:
│     sensitive = true
╵

Fixes #000

Changes proposed in the pull request:

• adding extra sensitive = true line into the above mentioned outputs to avoid running into this issue

[lonegunmanb]

Thanks @jvelasquez , LGTM!