feat!: configurable key to ID conversion

[erikwrede]

fixes #102 by giving users the choice to either convert all Key Columns to graphene.ID or leave all key columns as is.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (ae4f87c) 94.74% compared to head (4947030) 96.30%.

❗ Current head 4947030 differs from pull request most recent head cb5dcf7. Consider uploading reports for the commit cb5dcf7 to get more accurate results

Files	Patch %	Lines
graphene_sqlalchemy/converter.py	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #379      +/-   ##
==========================================
+ Coverage   94.74%   96.30%   +1.55%     
==========================================
  Files          10        9       -1     
  Lines        1333      921     -412     
==========================================
- Hits         1263      887     -376     
+ Misses         70       34      -36     

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[jendrikjoe]

Rest seems good. Maybe adding a test to ensure that actually querying an object returns as well the expected type (e.g. int not the converted id) might be helpful just for completeness 👍