[S3] inventory_configuration support

[zkarpinski]

Adds support for:

• put_bucket_inventory_configurations
• get_bucket_inventory_configuration
• list_bucket_inventory_configuration

** Including minor scaffolding fix to resolve #8726

[codecov]

Codecov Report

Attention: Patch coverage is 96.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 92.82%. Comparing base (fcb513c) to head (b73c55b).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
moto/s3/exceptions.py	75.00%	1 Missing ⚠️
moto/s3/models.py	95.65%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8785   +/-   ##
=======================================
  Coverage   92.82%   92.82%           
=======================================
  Files        1266     1266           
  Lines      110646   110696   +50     
=======================================
+ Hits       102704   102752   +48     
- Misses       7942     7944    +2     

Flag	Coverage Δ
servertests	28.08% <34.00%> (+<0.01%)	⬆️
unittests	92.79% <96.00%> (+<0.01%)	⬆️

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[bblommers]

LGTM - thanks for adding these features and for improving the scaffolding script @zkarpinski!