tikv: the calculation of raft-log-gc-count-limit should be based on 1 KiB instead of 1 MiB (#21966)

Author: King-Dylan

tikv-configuration-file.md

@@ -762,7 +762,7 @@ Configuration items related to Raftstore.
 ### `raft-log-gc-count-limit`
 
 + The hard limit on the allowable number of residual Raft logs
-+ Default value: the log number that can be accommodated in the 3/4 Region size (calculated as 1MiB for each log)
++ Default value: the number of logs that can fit into three-fourths of the Region size, calculated assuming each log is 1 KiB
 + Minimum value: `0`
 
 ### `raft-log-gc-size-limit`