Allow dynamic serializer configuration via settings

[massaroPietro]

• Added support for configuring serializers through settings: "SERIALIZERS" dictionary in djoser settings. Specifically added "provider_auth": "djoser.social.serializers.ProviderAuthSerializer".
• Updated ProviderAuthView to use the dynamic serializer: serializer_class = settings.SERIALIZERS.provider_auth

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.03%. Comparing base (35c815f) to head (c8a6155).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #832 +/- ## ========================================== - Coverage 99.03% 99.03% -0.01% ========================================== Files 26 26 Lines 833 832 -1 ========================================== - Hits 825 824 -1 Misses 8 8 ```

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