feat: add <Table/>

[ta1m1kam]

This PR introduces support for Slack’s new Table Block to the jsx-slack library.
It adds three new components:

• <Table /> – represents a Slack table block
• <TableRow /> – defines each row
• <TableCell /> – defines each cell

Key points

Supports columnSettings (alignment and wrapping per column).
Added documentation and tests.
No breaking changes — only new components and exports.

Resolves: #326

Example

<Blocks>
  <Table columnSettings={[{ align: 'left' }, { align: 'right' }]}>
    <TableRow>
      <TableCell>Item</TableCell>
      <TableCell>Price</TableCell>
    </TableRow>
    <TableRow>
      <TableCell>Widget A</TableCell>
      <TableCell>$99.99</TableCell>
    </TableRow>
  </Table>
</Blocks>

[yhatt]

While simple Slack Block Kit porting might be fine with this, jsx-slack is a library designed to increase the productivity of Slack apps by adopting familiar notations from HTML. It would be appropriate to implement this after the discussion about the design: #326 (comment)