Add handling to leverage RSC prefetch outputs (#10390)

Implements handling for the RSC prefetch outputs when available that
were added in https://github.com/vercel/next.js/pull/54403

packages/next/src/utils.ts

@@ -236,6 +236,7 @@ type RoutesManifestOld = {
   rsc?: {
     header: string;
     varyHeader: string;
+    prefetchHeader?: string;
     contentTypeHeader: string;
   };
   skipMiddlewareUrlNormalize?: boolean;