Bayesian Decision Analysis (Posterior Predictive + Utility Function)

# Notebook proposal
**Title**: Bayesian Decision Analysis

## Why should this notebook be added to pymc-examples?
PyMC lacking an example of a Bayesian Decision Analysis, much in the style of an example in Stan's Users Guide (see reference). I could try to create a Notebook, if that's of interest.


# References
https://mc-stan.org/docs/stan-users-guide/example-decision-analysis.html
