Add DroQ

[asmith26]

Attempt at #340 (WIP)

[codecov]

Codecov Report

Merging #342 (3099def) into master (43e6769) will decrease coverage by 0.20%.
The diff coverage is 73.97%.

@@            Coverage Diff             @@
##           master     #342      +/-   ##
==========================================
- Coverage   92.69%   92.49%   -0.20%     
==========================================
  Files         109      111       +2     
  Lines        7141     7208      +67     
==========================================
+ Hits         6619     6667      +48     
- Misses        522      541      +19     

Files	Coverage Δ
d3rlpy/algos/qlearning/__init__.py	100.00% <100.00%> (ø)
d3rlpy/algos/qlearning/base.py	88.21% <100.00%> (+0.03%)	⬆️
d3rlpy/models/encoders.py	97.10% <100.00%> (+0.08%)	⬆️
d3rlpy/models/torch/encoders.py	93.58% <50.00%> (-0.57%)	⬇️
d3rlpy/algos/qlearning/torch/droq_impl.py	58.33% <58.33%> (ø)
d3rlpy/algos/qlearning/droq.py	73.46% <73.46%> (ø)

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[takuseno]

@asmith26 Thank you for the PR! The overall approach looks good to me. Let me know when this PR is ready for review.