[Feature] MBPO Support

[nicolas-dufour]

Description

Support for MBPO

Motivation and Context

MBPO is a sample efficient method that improves over SAC.

Types of changes

What types of changes does your code introduce? Remove all that do not apply:

• [x] Example (update in the folder of examples)

Checklist

Go over all the following points, and put an x in all the boxes that apply. If you are unsure about any of these, don't hesitate to ask. We are here to help!

• [x] I have read the CONTRIBUTION guide (required)