[Feature Request] Implement MBPO algorithm

[dtch1997]

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🚀 Feature

I would like to implement a model-based RL algorithm, MBPO proposed here.

Motivation

The proposed algorithm claims to be simpler and up to 10x as sample efficient as some other baselines like SAC.
This would be helpful in my own work too.

### Checklist

• [ x] I have checked that there is no similar issue in the repo (required)

[Miffyli]

This should be discussed in the contrib repo. Can you open up an issue here?

[dtch1997]

Okay I have opened an issue in the contrib repo here: Stable-Baselines-Team/stable-baselines3-contrib#43
Closing this issue now