Use pytorch lightning's seed everything to set seed

[mjayasur]

Fix #1111

[codecov]

Codecov Report

Merging #1151 (786684e) into master (9855238) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1151      +/-   ##
==========================================
- Coverage   90.68%   90.68%   -0.01%     
==========================================
  Files          95       95              
  Lines        7622     7621       -1     
==========================================
- Hits         6912     6911       -1     
  Misses        710      710              

Impacted Files	Coverage Δ
scvi/_settings.py	87.77% <100.00%> (-0.14%)	⬇️

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[adamgayoso]

We should be able to properly test this right?

1. Set the seed and train a model 1 epoch
2. Set the seed again and do the same
3. NN weights should be exactly the same