Add Simulations for APO Causal Contrast for ATE & ATTEs vs IRM results

We could add an additional set of results to validate the coverage of APO causal contrast with appropriate re-weighting for the ATE and ATTE estimators in a setting comparable to IRM ATE and ATTE results. Results should be added here https://docs.doubleml.org/doubleml-coverage/irm/apo.html#causal-contrast-coverage