feat: add secondary boot disks field to NodePool API

PiperOrigin-RevId: 610868066

google/container/v1beta1/cluster_service.proto

@@ -837,6 +837,9 @@ message NodeConfig {
   // Optional. Reserved for future use.
   bool enable_confidential_storage = 46
       [(google.api.field_behavior) = OPTIONAL];
+
+  // List of secondary boot disks attached to the nodes.
+  repeated SecondaryBootDisk secondary_boot_disks = 48;
 }
 
 // Specifies options for controlling advanced machine features.
@@ -5939,6 +5942,27 @@ message EnterpriseConfig {
   ClusterTier cluster_tier = 1 [(google.api.field_behavior) = OUTPUT_ONLY];
 }
 
+// SecondaryBootDisk represents a persistent disk attached to a node
+// with special configurations based on its mode.
+message SecondaryBootDisk {
+  // Mode specifies how the secondary boot disk will be used.
+  // This triggers mode-specified logic in the control plane.
+  enum Mode {
+    // MODE_UNSPECIFIED is when mode is not set.
+    MODE_UNSPECIFIED = 0;
+
+    // CONTAINER_IMAGE_CACHE is for using the secondary boot disk as
+    // a container image cache.
+    CONTAINER_IMAGE_CACHE = 1;
+  }
+
+  // Disk mode (container image cache, etc.)
+  Mode mode = 1;
+
+  // Fully-qualified resource ID for an existing disk image.
+  string disk_image = 2;
+}
+
 // Options for in-transit encryption.
 enum InTransitEncryptionConfig {
   // Unspecified, will be inferred as default -