Fix example in Twin column documentation

[owlet1997]

Environment

• Documentation version: 7.2
• Part of the documentation: Manual
• Existing page: https://doc.cuba-platform.com/manual-7.2/gui_TwinColumn.html

Description of the bug or enhancement

incorrect example of using TwinColumn

<data>
    <instance id="orderDc" class="com.company.sales.entity.Order" view="order-edit">
        <loader/>
        <collection id="productsDc" property="products"/>
    </instance>
    <collection id="allProductsDc" class="com.company.sales.entity.Product" view="_minimal">
        <loader>
            <query>
                <![CDATA[select e from sales_Product e]]>
            </query>
        </loader>
    </collection>
</data>
<layout>
    <twinColumn id="twinColumn"
                dataContainer="productsDc"
                property="name"
                optionsContainer="allProductsDc"/>
</layout>

after reproducing ClassCastException is thrown: also it will be great to add info about displaying instanceName of entity in component.

AR:

dataContainer = productsDc property = name

ER:

dataContainer = orderDc property = products