Adding SHbbyy signal cross sections by brute force

As the title suggests - adding SH signal cross-sections in the custom XS file for almost the entire mass grid (just using DSIDs for currently available DSIDs for now). Open to suggestions for a cleaner implementation, but, this allows us to change the XS to something custom per mass point in case we want to use realistic XS values, which will allow for significance dependent blinding strategies.