Allow to configure models through class kwargs

[Bobronium]

Change Summary

Allow to configure models through class kwargs

from pydantic import BaseModel

class Model(BaseModel, extra='allow'):
    foo: int
    bar: int

Related issue number

Closes #2330

Implementation details

Any kwargs that are passed into class and match attrs of BaseConfig will be included in config.
All unused kwargs will be passed to type untouched so #867 won't break.

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.md file added describing change
  (see changes/README.md for details)

[codecov]

Codecov Report

Merging #2356 (6996ffb) into master (fc18f8e) will decrease coverage by 0.80%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master    #2356      +/-   ##
==========================================
- Coverage   99.97%   99.17%   -0.81%     
==========================================
  Files          23       23              
  Lines        4500     4485      -15     
  Branches      909      909              
==========================================
- Hits         4499     4448      -51     
- Misses          1       27      +26     
- Partials        0       10      +10     

Impacted Files	Coverage Δ
pydantic/typing.py	83.01% <82.14%> (-16.41%)	⬇️
pydantic/_hypothesis_plugin.py	100.00% <100.00%> (ø)
pydantic/annotated_types.py	100.00% <100.00%> (ø)
pydantic/fields.py	100.00% <100.00%> (ø)
pydantic/schema.py	100.00% <100.00%> (ø)
pydantic/validators.py	100.00% <100.00%> (ø)
pydantic/version.py	88.23% <0.00%> (-11.77%)	⬇️
pydantic/env_settings.py	98.41% <0.00%> (-1.59%)	⬇️
pydantic/networks.py	98.52% <0.00%> (-1.48%)	⬇️
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fc18f8e...f9bfb30. Read the comment docs.

[samuelcolvin]

thank you so much, this is great.