Add table footer support

Problem/Motivation

tfoot element is lost during the conversion

Steps to reproduce

1. Go to
2. Open the source editing.
3. Paste the following markup:

<table>
    <thead>
        <tr>
            <th>Items</th>
            <th scope="col">Expenditure</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <th scope="row">Donuts</th>
            <td>3,000</td>
        </tr>
        <tr>
            <th scope="row">Stationery</th>
            <td>18,000</td>
        </tr>
    </tbody>
    <tfoot>
        <tr>
            <th scope="row">Totals</th>
            <td>21,000</td>
        </tr>
    </tfoot>
</table>

• Switch back to the editing mode.
• Switch back to the source editing mode.

Expected result

tfoot is preserved.

❌ Actual result

tfoot is lost and merged to tbody.

For Reference See Attached Issue :-

https://github.com/ckeditor/ckeditor5/issues/12952