Store number of trainable parameters in config for later use

[ant0nsc]

At the moment, the model summary code in generate_and_print_model_summary does not store any of its results. The number of trainable parameters is logged to AzureML, but not anywhere else. It would be helpful to store the key output of the model summary, the number of trainable parameters, inside the model config, or at some other place so that it can be accessed later: In particular, it is important when we create a model dashboard in a post-crossvalidation-hook

AB#3923