能否支持自定义快捷键 🙏

### 🏷 Version

| Package | Version |
| -------------- | ------- |
| @antv/s2 | 1.54.1 |
| @antv/s2-react | 1.46.0 |
| @antv/s2-vue | - |

### Sheet Type

- [x] PivotSheet
- [x] TableSheet
- [ ] GridAnalysisSheet
- [x] StrategySheet
- [ ] EditableSheet

### 🖋 Description

当前S2的默认多选快捷键为`Command/Ctrl+点击`，但是在我们的平台中，多选行为一律都是`Shift+点击`，为了实现交互行为统一，让S2也是Shift多选，能否支持自定义快捷键，形如
```js
const config = {
hotKeys: {
multiSelection: 'Shift'
},
};
```

### 🏞 What problem does this feature solve

更灵活的自定义快捷键，增强业务接入后的交互一致性

### 🧐 Suggest the API

| name | type | default | description |
| ---- | ---- | ------- | ----------- |
| - | - | - | - |

Start by locating the existing multi-selection shortcut handling in S2 and checking how it applies to PivotSheet, TableSheet, and StrategySheet. Define how a configurable modifier should interact with the current Command/Ctrl behavior, then verify that Shift-based multi-selection works consistently for the listed sheet types and that the configuration is documented.

Written by the indexing model from the issue text.