Add budget to k8s-infra-ii-sandbox

Add a defined budget to `k8s-infra-ii-sandbox` but also use the project
to experiment GCP budgets.

Ref: kubernetes#1375

Signed-off-by: Arnaud Meukam <[email protected]>

infra/gcp/clusters/projects/k8s-infra-ii-sandbox/budget.tf

@@ -0,0 +1,41 @@
+/*
+
+This file contains 
+- defined budget for this project
+- notification channel when threshold is reached
+*/
+
+resource "google_billing_budget" "budget" {
+  billing_account = data.google_billing_account.account.id
+  display_name    = "Billing Budget for ${google_project.project.id}"
+
+  budget_filter {
+    projects = ["projects/${google_project.project.number}"]
+  }
+
+  amount {
+    specified_amount {
+      units = "1000"
+    }
+  }
+
+  threshold_rules {
+    threshold_percent = 0.9 // Threshold of 90% of the budget set
+  }
+
+  all_updates_rule {
+    monitoring_notification_channels = [
+      google_monitoring_notification_channel.wg_k8s_infra_leads.id,
+    ]
+    disable_default_iam_recipients = true
+  }
+}
+
+resource "google_monitoring_notification_channel" "wg_k8s_infra_leads" {
+  display_name = "Example Notification Channel"
+  type         = "email"
+
+  labels = {
+    email_address = "[email protected]"
+  }
+}