fixing issues in onnx tutorial to embed new models into HSSM

[gingjehli]

some important notes on this tutorial:
https://lnccbrown.github.io/HSSM/tutorials/blackbox_contribution_onnx_example/#loading-the-network

Most importantly:
It looks like parameter names for any new model cannot include underscores (“_”) in their labels. When using the .HSSM function to compile the model, parameters with underscores are not recognized and cause failures.
Additionally, p_outlier needs to be set to a value greater than zero; otherwise, it also triggers an error.

[AlexanderFengler]

#754