Consider checking TX load when serving thumbnails too

[daniil-berg]

We are currently checking the TX load of the storage node, whenever it has to serve a video file itself (i.e. does not redirect to a distributor). If it exceeds the max_load_file_serving threshold, we respond with a 503.

videbo/src/videbo/storage/http_util.py

Lines 243 to 251 in e7b53e0

	if request.http_range.start is not None and request.http_range.start > 0:
	# Never redirect requests for later parts of the video
	ensure_acceptable_load(tx_load, log=log)
	return # Serve file
	node, has_complete_file = dist_controller.get_node_to_serve(file)
	if node is None:
	# Found no distributor node that has the file or is downloading it
	ensure_acceptable_load(tx_load, log=log)
	return # Serve file

We do not do the same thing for thumbnails, which are always served by the storage node. I think for consistency, we probably should. @MartinGauk, what do you think?