[RFC] Add rules with URL schema

## 通过 URL schema 的方式添加规则

例如通过

```
lightproxy://request=add-rule&content=${encodeContent}
```

请求向 LightProxy 添加一条规则

## Add rules by URL schema

For example by

```
lightproxy://request=add-rule&content=${encodeContent}
```

Request to add a rule to LightProxy

The issue names no files, tests, or entry points. Start by locating LightProxy's URL-scheme handling and rule-creation entry point, then determine how the encoded content should be passed; done means a lightproxy://request=add-rule URL adds the supplied rule.

Written by the indexing model from the issue text.