v8.1.2: dynamic config add import.num-threads (#19716)

dynamic-config.md

@@ -234,6 +234,7 @@ The following TiKV configuration items can be modified dynamically:
 | storage.flow-control.soft-pending-compaction-bytes-limit | The threshold of kvDB pending compaction bytes that triggers flow control mechanism to reject some write requests |
 | storage.flow-control.hard-pending-compaction-bytes-limit | The threshold of kvDB pending compaction bytes that triggers flow control mechanism to reject all write requests |
 | `storage.scheduler-worker-pool-size` | The number of threads in the Scheduler thread pool |
+| `import.num-threads` | The number of threads to process restore or import RPC requests (dynamic modification is supported starting from v8.1.2) |
 | `backup.num-threads` | The number of backup threads (supported since v4.0.3) |
 | `split.qps-threshold` | The threshold to execute `load-base-split` on a Region. If the QPS of read requests for a Region exceeds `qps-threshold` for 10 consecutive seconds, this Region should be split.|
 | `split.byte-threshold` | The threshold to execute `load-base-split` on a Region. If the traffic of read requests for a Region exceeds the `byte-threshold` for 10 consecutive seconds, this Region should be split. |