PD can not identify hot region if region report interval greater than 10s period

## Feature Request
if region report interval more than 10s, pd will idenfy this region as col. So the hot region scheduler will not take effect because it has no hot region.
### Describe your feature request related problem
run:
1. go-tpc tpcc -H xxxx.xxx.xxx-P 4000 -D tpcc5k --warehouses 5000 --threads=128 run --time 36000s --threads=256
hot region scheduler can not work.
2. stop hot region scheduler
3. grant all hot region to some store(3h)
4. start hot region scheduler

I set strict as false and read priority as [query,bytes].
I has set report threshold as 1/4 of origin's and adjust cold time as 10 of origin's.

the first query store has less hot region and these regions has tiny hot degree. So pd will not balance them because of [min-hot-byte-rate,min-hot-key-rate,min-hot-query-rate]

### Describe the feature you'd like
1. it should has some tools to analyze the region report frequence
2. some threshold should be adjust if the hotest store do not identify any region.

### Describe alternatives you've considered

### Teachability, Documentation, Adoption, Migration Strategy