[MM-53454] Add export file settings + slash command for public link (#23915)

Co-authored-by: Mattermost Build <build@mattermost.com>

server/cmd/mmctl/docs/mmctl_export.rst

@@ -40,6 +40,7 @@ SEE ALSO
 * `mmctl export create <mmctl_export_create.rst>`_ 	 - Create export file
 * `mmctl export delete <mmctl_export_delete.rst>`_ 	 - Delete export file
 * `mmctl export download <mmctl_export_download.rst>`_ 	 - Download export files
+* `mmctl export generate-presigned-url <mmctl_export_generate-presigned-url.rst>`_ 	 - Generate a presigned url for an export file. This is helpful when an export is big and might have trouble downloading from the Mattermost server.
 * `mmctl export job <mmctl_export_job.rst>`_ 	 - List, show and cancel export jobs
 * `mmctl export list <mmctl_export_list.rst>`_ 	 - List export files