tikv: add a new dynamic config (#9672)

Author: Oreoxmt

dynamic-config.md

@@ -122,6 +122,7 @@ The following TiKV configuration items can be modified online:
 
 | Configuration item | Description |
 | :--- | :--- |
+| log.level | The log level. |
 | `raftstore.raft-max-inflight-msgs` | The number of Raft logs to be confirmed. If this number is exceeded, the Raft state machine slows down log sending. |
 | `raftstore.raft-log-gc-tick-interval` | The time interval at which the polling task of deleting Raft logs is scheduled |
 | `raftstore.raft-log-gc-threshold` | The soft limit on the maximum allowable number of residual Raft logs |