Add algorithm MAP-Elites-ES to QDax

[manon-but-yes]

Related to #81

This PR adds MAP-Elites-ES to QDax. The complete MAP-Elites-ES algorithm is implemented as an emitter, including the biased sampling from the repertoire, in qdax/core/emitters/mees_emitter.py.

qdax/utils/sampling.py also provide necessary functions to perform reevaluations of a given individual. In the case of MAP-Elites-ES this is needed to perform the 30 reevaluations of the final controller generated through ES.

[codecov-commenter]

Codecov Report

Merging #88 (211e86f) into develop (46e82b6) will increase coverage by 0.43%. The diff coverage is 97.73%.

@@             Coverage Diff             @@
##           develop      #88      +/-   ##
===========================================
+ Coverage    90.69%   91.13%   +0.43%     
===========================================
  Files           84       88       +4     
  Lines         4677     4986     +309     
===========================================
+ Hits          4242     4544     +302     
- Misses         435      442       +7     

Impacted Files	Coverage Δ
qdax/core/emitters/mees_emitter.py	95.83% <95.83%> (ø)
qdax/utils/sampling.py	100.00% <100.00%> (ø)
tests/baselines_test/mees_test.py	100.00% <100.00%> (ø)
tests/utils_test/sampling_test.py	100.00% <100.00%> (ø)

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