DOC: update doxygen of MachineLearningModel derived classes

Code/Learning/otbLibSVMMachineLearningModel.h

Code/Learning/otbMachineLearningModel.h

...iesAdapters/OpenCVAdapters/otbBoostMachineLearningModel.h

...ters/OpenCVAdapters/otbDecisionTreeMachineLearningModel.h

...enCVAdapters/otbGradientBoostedTreeMachineLearningModel.h

...OpenCVAdapters/otbKNearestNeighborsMachineLearningModel.h

...ers/OpenCVAdapters/otbNeuralNetworkMachineLearningModel.h

...pters/OpenCVAdapters/otbNormalBayesMachineLearningModel.h

...ers/OpenCVAdapters/otbRandomForestsMachineLearningModel.h

...itiesAdapters/OpenCVAdapters/otbSVMMachineLearningModel.h