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

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

server/channels/api4/export_local.go

@@ -7,4 +7,5 @@ func (api *API) InitExportLocal() {
 	api.BaseRoutes.Exports.Handle("", api.APILocal(listExports)).Methods("GET")
 	api.BaseRoutes.Export.Handle("", api.APILocal(deleteExport)).Methods("DELETE")
 	api.BaseRoutes.Export.Handle("", api.APILocal(downloadExport)).Methods("GET")
+	api.BaseRoutes.Export.Handle("/presign-url", api.APILocal(generatePresignURLExport)).Methods("POST")
 }