Add support of footer for x-table

[ivanchanfy]

I currently can't find a way to add tfoot to a table without modifying the Table component itself. Please add something like x-slot:footer for x-table.

Suggestion:

<x-table :headers="$headers" :rows="$rows">
    <x-slot:footer>
        <tr>
            <th>Col 1</th>
            <th>Col 2</th>
        </tr>
    </x-slot:footer>
</x-table>

[ivanchanfy]

Do you think it's possible to add support for sticky columns at the same time?
I'm working on a project that needs mobile optimization and I think a sticky column is a good idea.