[redis_proxy] added a constraint for route.prefix().size() (#12637)

Signed-off-by: jianwen <jianwendong@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 7852b9d98e5cc07856f316047091490d315f0332

envoy/extensions/filters/network/redis_proxy/v3/redis_proxy.proto

@@ -156,7 +156,7 @@ message RedisProxy {
 
       // String prefix that must match the beginning of the keys. Envoy will always favor the
       // longest match.
-      string prefix = 1;
+      string prefix = 1 [(validate.rules).string = {max_bytes: 1000}];
 
       // Indicates if the prefix needs to be removed from the key when forwarded.
       bool remove_prefix = 2;