lightning physical should check the TiDB and PD address in config are in the same cluster

## Enhancement

as title. Because physical import will read table structure from TiDB and import data to PD/TiKV. Lightning should make sure table structure and table data are consistent, which means TiDB and PD/TiKV should in the same cluster.

We still allow these behaviours
- If PD address is omitted, lightning will use TiDB HTTP API `/settings` to get PD address when boot up
- PD address can still be manually specified, in case that PD node has multiple addresses like external and internal addresses, and lighting should access only one of them