In disk_channel queues synchronously push to disk on shutdown (#18415) (#18788)

Partial Backport of #18415

Instead of using an asynchronous goroutine to push to disk on shutdown
just close the datachan and immediately push to the disk.

Prevents messages of incompletely flushed queues.

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/queue/queue_disk_channel_test.go

@@ -188,5 +188,4 @@ func TestPersistableChannelQueue(t *testing.T) {
 	for _, callback := range callbacks {
 		callback()
 	}
-
 }