De string queries

[PierreBoyeau]

Fixes #1040

[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.70%. Comparing base (19b9c4f) to head (26c04ee).

Files	Patch %	Lines
scvi/model/base/_utils.py	94.73%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1041      +/-   ##
==========================================
- Coverage   90.70%   90.70%   -0.01%     
==========================================
  Files          90       90              
  Lines        6607     6615       +8     
==========================================
+ Hits         5993     6000       +7     
- Misses        614      615       +1     

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[adamgayoso]

We need to change the docstring in rnamixin, totalvi de function and I think peakvi.