Scope using `MediaTransformation` and `MediaConfigList` in `MMM` class

[wd60622]

Following #968, both MediaTransformation and MediaConfigList are following the same API which it easier to use them in the MMM.

However, there will be some API changes in order to make this happen. Some initial items that will have to be check are:

• What happens to the current adstock, saturation, and adstock_first initialization parameters?
• Should adstock and saturation attributes be kept? What is the result when there are multiple MediaTransformation objects?
• How will the optimizer work with the new API?
• How will existing plotting functions work?
• Will all the priors be passed into the model_config attribute? or just kept in the media transformation object itself?

Some items that would go:

• forward_pass method makes used __call__ method. MediaTransformation(...)()