feat(data-table): dispatch on:click:header--select event

[metonym]

Follow-up to #1450

#1450 added a dispatched event click:row--select for selectable rows.

This PR adds an additional event when using a batch selectable DataTable, where clicking the checkbox in the header will either select or deselect all rows. A similar event would be click:header--expand for a batch expandable DataTable.

Compared to click:row--select, one difference in the e.detail API is that the checkbox state can be indeterminate.

// indeterminate
0 < n < rows.length - 1

Sample usage

<DataTable
  batchSelection
  on:click:header--select={(e) => {
    console.log("header--select", e.detail.selected); // boolean
    console.log("header--select", e.detail.indeterminate); // boolean
  }}
/>

[metonym]

Released in v0.69.0