Adding a handicap group to a set already containing one or more entities might fail

[carltonwhitehead]

I ran into an issue while building out the analogous feature for competition groups, and I suspect the same problem exists on the handicap group side.

Remove the MapStruct uses link between the HandicapGroupSetMapper and HandicapGroupMapper, and then supply the a HandicapGroupSetDao and HandicapGroupMapper when the MapStructModule provides the instance, and glue them together like so: https://github.com/caeos/coner-core/commit/7be623ef83e3f9316e4d870136eabe12031fe70a