[Feature Request] 周(datePicker)组件的value值能否配置？Can the value of the datePicker(week) component be configured?

### Existing Component
是

### Component Name
datePicker

### Description
目前周组件的value比较怪异，绑定的是第二列的value，`value-format`和`format`都是这个值且不支持function，符合逻辑和当前ui的做法是返回第一列的值，希望能够更改(最好是可配置的)。

At present, the value of the datePicker(week) component is weird, and it is bound to the value of the second column. `value-format` and `format` both bind this value and do not support function. The logical and current UI approach is to return the value of the first column, hoping to change it(preferably configurable).