MMM Multi-Dimensional Example (#1521)

* init

* trying replicate example

* priors

* refine priors

* cleanup

* improvements

* add to docs

* rm divergences

* rerun

* cleanup

* allow kwargs

* try out of sample

* fix out of sample coords control

* out of sample original scale

* rerun

* undo

* re-run

* add text

* rm

Author: juanitorduz

docs/source/notebooks/index.md

@@ -16,6 +16,7 @@ mmm/mmm_counterfactuals
 mmm/mmm_evaluation
 mmm/mmm_example
 mmm/mmm_lift_test
+mmm/mmm_multidimensional_example
 mmm/mmm_roas
 mmm/mmm_time_slice_cross_validation
 mmm/mmm_time_varying_media_example