Separate model configuration notebook into two

[wd60622]

The model configuration notebook includes both Prior class overview and model configuration.
It might be better to separate these into two notebooks making Prior class overview shown in tab:

pymc-marketing/docs/source/notebooks/index.md

Line 47 in 9bae8a0

general/model_configuration

The new notebook might be "Prior class and variable specification" which could include items about:

• Prior class and Censored class
• VariableFactory protocol class and extension