prop224: Rate limit HS descriptor reuploads
prop224 services currently re-upload their HS descriptor everytime they receive new dir info (descriptors) if they are close to 100% visibility of the network.
This is done to make sure we always publish to the right HSDir nodes, but it could also lead to uploading lots of descriptors in a small time frame.
A good fix for this would be to cache the previous set of responsible HSDirs (maybe on the desc), and avoid reuploading the same descriptor if the set of HSDirs is the same even if we received new dirinfo.
Also we should probably add a cache to avoid publishing the same descriptor multiple times in a small timeframe anyway.