Subissue: Consolidate OpenAI providers

[andrii-i]

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Problem

Currently there are 3 OpenAI providers: openai, openai-chat, openai-chat-new. This is confusing, the same service by the same company shouldn’t have 3 different provider IDs.

Proposed Solution

Ideally, consolidate all OpenAI providers into a single provider (for example, openai).

Additional context

Note that openai-chat:gpt-3.5-turbo and openai-chat-new:gpt-3.5-turbo is the same model.

[JasonWeill]

To avoid breaking older notebooks, we should treat calls to openai-chat or openai-chat-new as calls to openai models after this is fixed.

[dlqqq]

We should explore allowing one model provider to refer to multiple LangChain classes in v3. Adding this issue to the milestone.