qps keep falling to zero until the fault recovered when injection pd leader io delay 500ms last for 10mins，we need some tuning parameters for this issue

## Bug Report

### What did you do?
1、run tpcc
2、injection pd leader io delay 500ms last for 10mins

### What did you expect to see?
qps can recover within 5mins

### What did you see instead?
qps keep falling to zero which last for 10mins until the fault recovered

### What version of PD are you using (`pd-server -V`)?
./pd-server -V
Release Version: v8.5.0-alpha-32-g90cc61b4
Edition: Community
Git Commit Hash: 90cc61b432feb3744cc71aa82bd55785e4646396
Git Branch: HEAD
UTC Build Time: 2024-11-21 08:41:25
2024-11-22T03:48:28.199+0800