add ability to benchmark via synth validation

[IyarLin]

Proposed changes

This PR adds the ability to benchmark causal inference algorithms on specific datasets of interest by implementing the approach outlined at "Schuler, A., Jung, K., Tibshirani, R., Hastie, T., and Shah, N. Synth-validation: Selecting the best causal inference method for a given dataset (2017)" https://arxiv.org/pdf/1711.00083

Usage of this functionality is demonstrated in docs/examples/benchmark_semi_synthetic_simulation_studies.ipynb

I've built the docs locally.

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[ras44]

might want to update the docs, specifically docs/examples/ to include this new contribution- thanks!

[IyarLin]

@ras44 I have added a notebook demonstrating the added functionality at docs/examples/benchmark_semi_synthetic_simulation_studies.ipynb

I've also built the docs locally though I didn't see it added anything to the PR.

If I'm still missing some docs please let me know how to add those as I didn't find anything under the contribution guidelines.

Thanks!

[jeongyoonlee]

Thanks for the contribution, @IyarLin. You can add the link to your notebook to docs/examples.rst to show it on the documentation website.

[IyarLin]

@jeongyoonlee @ras44 I've added the notebook demonstrating the added functionality to docs/examples.rst
Let me know if there's anything else missing

[ras44]

LGTM, thanks for your contribution 👍