Sentinel限流等规则一键导出json功能

## Issue Description

feature request

### Describe what happened (or what feature you want)
比如说这样的场景，我们使用Nacos做Sentinel的持久化，但是需要在Nacos配置里面写上Sentinel的限流熔断等规则(json格式)，但是写这样的json很容易出错，一般是在Sentinel网页界面配置好了规则，然后如果在网页界面有个导出json格式功能，这样就可以直接复制过去了，非常方便且不容易出错。

### Describe what you expected to happen

### How to reproduce it (as minimally and precisely as possible)

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### Tell us your environment

### Anything else we need to know?

Start by reviewing the Sentinel web interface entry point and the Nacos persistence configuration described in the issue. Determine how the configured flow-control and circuit-breaking rules are represented, then define the export behavior so the resulting JSON can be copied directly into Nacos. Done means the interface can export the relevant rules in valid JSON.

Written by the indexing model from the issue text.