dumpling: support `tidb_enable_paging` to `ON` by default to save memory

[lichunzhu]

Enhancement

https://docs.pingcap.com/tidb/dev/system-variables#tidb_enable_paging-new-in-v540
TiDB has already supported tidb_enable_paging to save memory for dumping cases. Dumpling can set this to ON for TiDB >= v6.2.0 by default to save memory usage.