辛苦评估增加并发线程数流量控制和冷启动流量整形效果

[zxb448126]

What is the feature you want to add?
详细可以参见sentinel官方文档说明，辛苦帮忙评估完善，进一步提高北极星的流量治理能力~

Why do you want to add this feature?

How to implement this feature?

Additional context
Add any other context or screenshots about the feature request here.

[andrewshan]

根据3月底例会的结论：#915
用户需求合理，可以接纳

[chuntaojun]

该 issue 需要先定义相关治理规则 spec，https://github.com/polarismesh/specification，如果愿意参与的开发者可以先把 spec 定义提交下，然后在进行开发