chore: update default origings CORS policy for dev UI

The current defaults are very restrictive and so you're met with CORS errors when you use Cloud Run to host the dev ui and try to interact with it. For anything beyond a prototype these defaults should be overwritten.

PiperOrigin-RevId: 820808616

Author: Poggecci

dev/src/main/java/com/google/adk/web/config/AdkWebCorsProperties.java

@@ -34,7 +34,7 @@ public record AdkWebCorsProperties(
 
   public AdkWebCorsProperties {
     mapping = mapping != null ? mapping : "/**";
-    origins = origins != null && !origins.isEmpty() ? origins : List.of();
+    origins = origins != null && !origins.isEmpty() ? origins : List.of("*");
     methods =
         methods != null && !methods.isEmpty()
             ? methods