[models] Add support for learning rate schedulers

src/mednet/libs/classification/config/models/alexnet.py

...t/libs/classification/config/models/alexnet_pretrained.py

src/mednet/libs/classification/config/models/densenet.py

.../libs/classification/config/models/densenet_pretrained.py

src/mednet/libs/classification/config/models/densenet_rs.py

src/mednet/libs/classification/config/models/pasa.py

src/mednet/libs/classification/models/alexnet.py

...mednet/libs/classification/models/classification_model.py

src/mednet/libs/classification/models/densenet.py

src/mednet/libs/classification/models/pasa.py

src/mednet/libs/common/engine/callbacks.py

src/mednet/libs/common/models/model.py

src/mednet/libs/segmentation/config/models/driu.py

src/mednet/libs/segmentation/config/models/driu_bn.py

src/mednet/libs/segmentation/config/models/driu_od.py

src/mednet/libs/segmentation/config/models/driu_pix.py

src/mednet/libs/segmentation/config/models/hed.py

src/mednet/libs/segmentation/config/models/lwnet.py

src/mednet/libs/segmentation/config/models/m2unet.py

src/mednet/libs/segmentation/config/models/unet.py