[node operator] Add GCP client

Signed-off-by: Malte Poll <mp@edgeless.systems>

operators/constellation-node-operator/internal/gcp/client/metadata.go

@@ -0,0 +1,21 @@
+package client
+
+import (
+	computepb "google.golang.org/genproto/googleapis/cloud/compute/v1"
+)
+
+// getMetadataByKey returns the value of the metadata key in the given metadata.
+func getMetadataByKey(metadata *computepb.Metadata, key string) string {
+	if metadata == nil {
+		return ""
+	}
+	for _, item := range metadata.Items {
+		if item.Key == nil || item.Value == nil {
+			continue
+		}
+		if *item.Key == key {
+			return *item.Value
+		}
+	}
+	return ""
+}