[OneDiscover] Enable columns sorting by draggable column header

[kertal]

📓 Summary

Once draggable column headers are available in Kibana https://github.com/elastic/eui/pull/8015, Discover's UnifiedDatable should make use of this new neat functionality. It allows to sort columns of Discover's data table by drag&drop directly on the header, without the need to got to the Columns popover.

✔️ Acceptance criteria

• The columns in Discover should be sortable by drag and drop of the tables column headers
• There should be functional coverage dragand drop table column headers

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)