token-limit 配置项最大值不合理

[x-ainger]

File: /release-7.5/tidb-configuration-file.md

最大值（64 位平台）：18446744073709551615
最大值（32 位平台）：4294967295

相关代码：
func NewTokenLimiter(count uint) *TokenLimiter {
tl := &TokenLimiter{count: count, ch: make(chan *Token, count)}
for i := uint(0); i < count; i++ {
tl.ch <- &Token{}
}

return tl

}

TiDB运行时，会初始化指定长度的 channel，若设置过大，会导致 TiDB OOM 无法启动。建议限制该配置项的最大值

[Oreoxmt]

@djshow832 Could you please take a look at this issue? Thanks!

[djshow832]

I have filed an issue for TiDB: pingcap/tidb#53312

Currently, we have 2 ways to fix the doc:

1. Fix the issue on TiDB and then update the value in docs for branch dev (I don't think this bugfix needs to be cherry-picked into previous versions)
2. Recommend the users to set the value according to the memory of the machine and warn them

[djshow832]

After discussion, we chose the 1st solution.