Add a 'copy to clipboard' option to the column menu in the new Table view

[aarju]

Describe the feature:
In the new Table view there currently (7.13) isn't an easy way to highlight and copy the column header field with the field name. It would be nice if the column dropdown menu contained a 'copy to clipboard' option to copy the name of the field to the clipboard.

Describe a specific use case for the feature:
A user is collaborating with someone via email or slack and they want to copy the field names from Kibana they can use this option to quickly copy the field names to the clipboard.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)