Allow setting max-weight-norm optimizer parameter

[jimypbr]

[From AlexC in GC] The reference implementation uses a value of 10 for this parameter. However the implementation in GC-Optimum passes None, with no possibility for the user to set this parameter

• create training command line option --max-weight-norm it can default to None for backwards compatibility
• in IPUTrainer.create_optimizer pass this argument to LAMB optimizer as part of optimizer_kwargs