Quarkus REST - Be more permissive when adding headers

The JAX-RS API is very loose and allows adding Object and in some cases
we actually add a List to the headers and we need to take this into
account.

While I'm usually not for handling things this way, the API is not
enforcing things properly so I think we really need to handle this
ourself.

Fixes #47507

Author: gsmet

independent-projects/resteasy-reactive/common/runtime/src/main/java/org/jboss/resteasy/reactive/common/jaxrs/AbstractResponseBuilder.java

@@ -277,11 +277,16 @@ public Response.ResponseBuilder cacheControl(CacheControl cacheControl) {
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public Response.ResponseBuilder header(String name, Object value) {
         if (value == null) {
             metadata.remove(name);
             return this;
         }
+        if (value instanceof List values) {
+            metadata.addAll(name, values);
+            return this;
+        }
         metadata.add(name, value);
         return this;
     }