[feature request] El select can add an attribute to configure the change event. The selected value returns the value of rule or label and value

### Existing Component
是

### Component Name
Select

### Description
el-select可以增加一个属性来配置change事件选中值返回vaule或者label和value，例如配置label-value=”true“时，change事件返回值为：{”label“: "名称", "value": "name"}，默认情况不配置此属性只返回value: name