Feature/dv3 imagination notebook

[belerico]

Summary

This PR adds a new notebook in which we describe how to generate a video (both from imagination and by reconstruction) from a trained Dreamer-V3 agent. Closes #211

Type of Change

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• New feature (non-breaking change that adds functionality)

Checklist

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• I have tested my changes locally and they work as expected. (Please describe the tests you performed.)
• I have added unit tests for my changes, or updated existing tests if necessary.
• I have updated the documentation, if applicable.
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