Implementation of reinvent RL objective for goal-directed design

[maclandrol]

Changelogs

• Add implementation of the various variant of REINVENT, while following trl interface for PPO.
• Add tutorials for goal-directed optimization with REINVENT implementation

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Checklist:

• [ ] Add tests to cover the fixed bug(s) or the new introduced feature(s) (if appropriate).
• [x] Update the API documentation if a new function is added, or an existing one is deleted. Eventually consider making a new tutorial for new features.
• [ ] Write concise and explanatory changelogs below.
• [x] If possible, assign one of the following labels to the PR: feature, fix or test (or ask a maintainer to do it for you).

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Implementation of the REINVENT optimization algorithm in SAFE.