fix(@angular-devkit/build-angular): ensure route has leading slash in prerender builder

Ensures that the route always starts with a leading slash when calling the render function, preventing potential issues with relative paths or incorrect URL resolution during prerendering.

(cherry picked from commit 30d8332)

Author: alan-agius4

packages/angular_devkit/build_angular/src/builders/prerender/index.ts

@@ -217,7 +217,7 @@ async function _renderUniversal(
               inlineCriticalCss: !!normalizedStylesOptimization.inlineCritical,
               minifyCss: !!normalizedStylesOptimization.minify,
               outputPath,
-              route,
+              route: route[0] === '/' ? route : '/' + route,
               serverBundlePath,
             };