MMCTL: Add import delete cmd for removing the import files (#29764)

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>

server/cmd/mmctl/docs/mmctl_import.rst

@@ -37,6 +37,7 @@ SEE ALSO
 ~~~~~~~~
 
 * `mmctl <mmctl.rst>`_ 	 - Remote client for the Open Source, self-hosted Slack-alternative
+* `mmctl import delete <mmctl_import_delete.rst>`_ 	 - Delete an import file
 * `mmctl import job <mmctl_import_job.rst>`_ 	 - List and show import jobs
 * `mmctl import list <mmctl_import_list.rst>`_ 	 - List import files
 * `mmctl import process <mmctl_import_process.rst>`_ 	 - Start an import job