Wrapper for fixed initial state of environments

[limbryan]

The wrapper alters the reset function to return the default initial joint positions and zero velocity on the joints. Some issues remain due to the underlying brax envs which do not have uniform api for _get_obs.

• tests have been implemented, fails the humanoid, walker and hopper tests at the moment because of the issue mentioned above.

[codecov-commenter]

Codecov Report

Merging #92 (ebd6af0) into develop (ab4d4ca) will increase coverage by 1.00%. The diff coverage is 87.12%.

@@             Coverage Diff             @@
##           develop      #92      +/-   ##
===========================================
+ Coverage    89.68%   90.69%   +1.00%     
===========================================
  Files           68       84      +16     
  Lines         3957     4673     +716     
===========================================
+ Hits          3549     4238     +689     
- Misses         408      435      +27     

Impacted Files	Coverage Δ
qdax/environments/__init__.py	89.79% <83.33%> (-0.91%)	:arrow_down:
tests/environments_test/wrapper_test.py	86.66% <86.66%> (ø)
qdax/environments/init_state_wrapper.py	90.00% <90.00%> (ø)
tests/baselines_test/sac_test.py	98.21% <0.00%> (ø)
tests/environments_test/pointmaze_test.py	100.00% <0.00%> (ø)
qdax/tasks/standard_functions.py	100.00% <0.00%> (ø)
tests/default_tasks_test/brax_task_test.py	97.14% <0.00%> (ø)
qdax/tasks/qd_suite/__init__.py	100.00% <0.00%> (ø)
tests/default_tasks_test/qd_suite_test.py	92.68% <0.00%> (ø)
qdax/tasks/brax_envs.py	88.33% <0.00%> (ø)
... and 15 more

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[felixchalumeau]

After discussions, we decided to revert the last commit to come back to the previous design.