fixing OSS filter_fuzz_test OOM issue when thread_count is 800 million. (#23782)

Signed-off-by: Yanjun Xiang <yanjunxiang@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 9db77e66e208f5bc72a3155cbf3f9dbd87cd6e12

envoy/extensions/common/async_files/v3/async_file_manager.proto

@@ -22,7 +22,7 @@ message AsyncFileManagerConfig {
     // The number of threads to use. If unset or zero, will default to the number
     // of concurrent threads the hardware supports. This default is subject to
     // change if performance analysis suggests it.
-    uint32 thread_count = 1;
+    uint32 thread_count = 1 [(validate.rules).uint32 = {lte: 1024}];
   }
 
   // An optional identifier for the manager. An empty string is a valid identifier