Add DroQ

[asmith26]

Attempt at #340 (WIP)

[codecov]

Codecov Report

❌ Patch coverage is 73.97260% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.49%. Comparing base (43e6769) to head (3099def).
⚠️ Report is 207 commits behind head on master.

Files with missing lines	Patch %	Lines
d3rlpy/algos/qlearning/droq.py	73.46%	13 Missing ⚠️
d3rlpy/algos/qlearning/torch/droq_impl.py	58.33%	5 Missing ⚠️
d3rlpy/models/torch/encoders.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            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     

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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.