Breaking-IID baselines with global imbalance but w/o chunking

[mcw92]

Start runs for globally imbalanced datasets without chunking, i.e., with the globally_imbalanced flag set and mu_data = 0.5, 2.0, inf but the locally_imbalanced flag not set. These runs serve as a baseline for the breaking-IID experiments which use chunking of the global train data over all available nodes by default.