[Docs] OpenAI Integration docs for the website

[the-praxs]

📥 Pull Request

📘 Description

• Closes [Docs]: OpenAI documentation #470 and [Bug]: Type mismatch in OpenAI example notebook #548
• Adds a doc page for OpenAI with sync and async example codes for both streaming and non-streaming
• Minor changes to Anthropic and Cohere docs

🧪 Testing

• Previewed with mvintlify locally for the docs
• Tested the code examples locally

🗒️ TODO

• Add sections for openai<1.0.0 and openai>=1.0.0
• Add example notebook(s) for OpenAI similar to Anthropic
• Add a link in the examples/README.md

[the-praxs]

@areibman should I include a link to the example notebooks in the docs page?