Model fit parameters

[amaurs]

There should be a parameter that lets you pick a size to train the model. This would make easier to compare models. For instance:

antares model_fit -model rf \
                  -p landsat_8_madmex_002_jalisco_2017 \
                  -t persistent_test \
                  --region Jalisco \
                  --name amau_rf_landsat_8_madmex_002_jalisco_2017_persistent_test \
                  -sp mean \
                  -extra n_estimators=100 max_depth=20 \
                  --sample-size 100000

In case both --sample and --sample-size are specified an error should be thrown telling the user that those parameters can't be used at the same time.