refactor: split disabled models for endpoints mapping into chat completions endpoint-disabled and completions endpoint-enabled mappings

[PChaparro]

Describe the change

This PR refactors model mapping logic by splitting the original disabledModelsForEndpoints map into two distinct maps: disabledModelsForChatCompletionsEndpoint and enabledModelsForDeprecatedCompletionsEndpoint.

This improves clarity and simplifies future maintenance of model support across endpoints.

Provide OpenAI documentation link

• https://platform.openai.com/docs/models
• https://platform.openai.com/docs/api-reference/completions
• https://platform.openai.com/docs/api-reference/chat/create

Describe your solution

• Created disabledModelsForChatCompletionsEndpoint to list models not supported by the chat completions endpoint. Maintaining a deny list is simpler since most new models are supported by chat completions by default.

• Created enabledModelsForDeprecatedCompletionsEndpoint to list models that are supported by the legacy completions endpoint. Maintaining an allow list is more appropriate here, since the completions endpoint is deprecated and no longer widely supported.

Tests

Executed the verification command provided in the CONTRIBUTING.md file. All tests passed successfully and the refactor did not introduce any regressions.

Issue: #972.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.43%. Comparing base (774fc9d) to head (5b57388).
Report is 90 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #974       +/-   ##
===========================================
- Coverage   98.46%   85.43%   -13.03%     
===========================================
  Files          24       43       +19     
  Lines        1364     2266      +902     
===========================================
+ Hits         1343     1936      +593     
- Misses         15      308      +293     
- Partials        6       22       +16     

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