Feat: add algo aurora

[felixchalumeau]

Related issues: #142

This PR introduces AURORA and PGA-AURORA, algorithms that define the behaviour descriptor in an unsupervised manner.

This PR introduces:

• unstructured repertoire
• aurora class
• utils to define an auto encoder with lstm
• test for aurora
• example for aurora and pga aurora
• updated readme and docs

Checks

• [x] a clear description of the PR has been added
• [x] sufficient tests have been written
• [x] relevant section added to the documentation
• [x] example notebook added to the repo
• [x] clean docstrings and comments have been written
• [x] if any issue/observation has been discovered, a new issue has been opened

Future improvements

We are pushing this PR to have the code open sourced for ICLR but some part of the code do not reach the code quality standard that we have been fixing for QDax until now. I will open an issue: we will need to clean this in the near future.

[codecov-commenter]

:warning: Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

Attention: Patch coverage is 92.87305% with 32 lines in your changes missing coverage. Please review.

Project coverage is 92.30%. Comparing base (b221c68) to head (6c5801e). Report is 15 commits behind head on develop.

Files with missing lines	Patch %	Lines
qdax/core/containers/unstructured_repertoire.py	83.47%	19 Missing :warning:
tests/core_test/aurora_test.py	90.32%	9 Missing :warning:
qdax/utils/train_seq2seq.py	95.58%	3 Missing :warning:
...x/core/neuroevolution/networks/seq2seq_networks.py	98.59%	1 Missing :warning:

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #144 +/- ## =========================================== + Coverage 92.28% 92.30% +0.01% =========================================== Files 120 125 +5 Lines 7055 7485 +430 =========================================== + Hits 6511 6909 +398 - Misses 544 576 +32 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[Lookatator]

@felixchalumeau, do you have any comment regarding all the refactoring that has been done? :smile: