[Deserialization] flatten configs cannot be deserialized by serde

[ZhiHanZ]

Summary

Query use flatten for configuration management, however, serde itself would not compile it and would NOT throw error information

Additional context
to relieve this issue, current approach is to parse each flattened areas separately which works for now, we should track on upstream for complete fixes or write down some encoding and decoding methods to avoid this issue
nox/serde_urlencoded#33

[Xuanwo]

Already addressed by newly designed config format.