Survival docs

[GStechschulte]

This PR adds a notebook explaining how to perform survival analysis in Bambi using the cat adoption dataset from chapter 11.4 of Richard McElreath's Statistical Rethinking. Sections include:

• explanation of survival and censoring data (including what right and left censoring is)
• survival functions and popular estimators (emphasis on Kaplan-Meirer estimator)
• regression models with survival responses and how the hazard rate and cox proportional hazards facilitate such an analysis
• explanation of the pm.Censored distribution with and without predictors
• two Bambi models (with and without predictors)

To do:

• finish the Regression models with survival responses section
• add summary section

Although there are a couple "to do" items, this docs example is far enough along I am opening this draft PR for feedback. Thanks! 🐱

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[tomicapretto]

As usual this is an amazing tutorial. Feel free to merge after you address the comments (or ping me if you need help!)

[GStechschulte]

As usual this is an amazing tutorial. Feel free to merge after you address the comments (or ping me if you need help!)

Thanks a lot!! Especially for the review. My only question is regarding the noise term (commented above).