[CI] Bump service pool node count/node spec

This patch bumps the number of nodes in the service pool from 2 to 3 and
additionally increases the spec of the machines from e2-small to
e2-highcpu-4. We were running into DNS issues due to a downed pod
that we believe was caused by a lack of resources in the service pool.
Adding an additional pod should help mostly with redundancy but also
with capacity in addition to the capacity increase within each node.

Author: boomanaiden154

premerge/main.tf

@@ -63,10 +63,10 @@ resource "google_container_node_pool" "llvm_premerge_linux_service" {
   name       = "llvm-premerge-linux-service"
   location   = "us-central1-a"
   cluster    = google_container_cluster.llvm_premerge.name
-  node_count = 2
+  node_count = 3
 
   node_config {
-    machine_type = "e2-small"
+    machine_type = "e2-highcpu-4"
   }
 }