Description of feature

Pass along arguments of the regression based models in _sa.py and write output to Andata object.
The current idea is to refactor the _regression_model function into a preparation step and call the model.fit function in the public function.

• refactor _regression_model to a preparation step

cox_ph

• add arguments of liefelines function
• write output to anndata object
• key_added keyword (work in progress) for new entries
• make everything after adata, duration_col keyword only ("*,")

weibull_aft

• add arguments of liefelines function
• write output to anndata object
• key_added keyword (work in progress) for new entries
• make everything after adata, duration_col keyword only ("*,")

log_logistic_aft

• add arguments of liefelines function
• write output to anndata object
• key_added keyword (work in progress) for new entries
• make everything after adata, duration_col keyword only ("*,")