BrianChen

use flat array for field indexing instead of hashmap

7

To resolve [KAG-5155](https://konghq.atlassian.net/browse/KAG-5155) [KAG-5155]: https://konghq.atlassian.net/browse/KAG-5155?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

metadata: Fix metadata request topic list length incorrect issue (#5049)

1

For metadata request API version >= 9, Null array length is not correctly set, the 4 bytes int should be replaced by 1 byte varint. Fix https://github.com/confluentinc/librdkafka/issues/5049

### Context I'm using kcat as kafka client, when running below command in shell `kcat -b 127.0.0.1:9092 -L -d metadata -X allow.auto.create.topics=true` the debug output shows that client will generate...