Model Tuner 0.0.20a

• Added flexibility between boolean and None for stratification inputs
• Added custom exception for non pandas inputs in return_bootstrap_metrics
• Enforced required model_type input to be specified as "classification" or "regression"
• Removed extraneous "=" print below pipeline_steps
• Handled missing pipeline_steps when using imbalance_sampler
• Updated requirements for python==3.11
• Fixed SMOTE for early stopping
• Removed extra model_type input from xgb_early_test.py