[Feature Request] Add perplexity API support

[DerekWongJC]

🥰 需求描述

Perplexity API provides advanced capabilities for search and conversational AI. Adding support for this API will enable users to leverage its features directly within ChatGPT-Next-Web, enhancing the platform's functionality and expanding its use cases.

🧐 解决方案

Adding a configuration option in the settings to input API keys for Perplexity.
Implementing API calls to Perplexity endpoints within the backend.
Creating a UI toggle or button to switch between OpenAI and Perplexity responses.
Ensuring compatibility with existing features like chat history and response formatting.

📝 补充信息

Documentation for Perplexity API can be referenced for implementation details.
This feature can attract users who rely on Perplexity's unique capabilities, further diversifying the platform's user base.

[BaksiLi]

N.B. The returned json has a list of citations

{
  "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "model": "llama-3.1-sonar-small-128k-online",
  "object": "chat.completion",
  "created": 1724369245,
  "citations": [
    "https://www.astronomy.com/science/astro-for-kids-how-many-stars-are-there-in-space/",
    "https://www.esa.int/Science_Exploration/Space_Science/Herschel/How_many_stars_are_there_in_the_Universe",
    "https://www.space.com/25959-how-many-stars-are-in-the-milky-way.html",
    "https://www.space.com/26078-how-many-stars-are-there.html",
    "https://en.wikipedia.org/wiki/Milky_Way",
    "https://www.littlepassports.com/blog/space/how-many-stars-are-in-the-universe/?srsltid=AfmBOoqWVymRloolU4KZBI9-LotDIoTnzhKYKCw7vVkaIifhjrEU66_5"
  ],
  "choices": [
    {
      "index": 0,
      "finish_reason": "stop",
      "message": {
        "role": "assistant",
        "content": "The number of stars in the Milky Way galaxy is estimated to be between 100 billion and 400 billion stars. The most recent estimates from the Gaia mission suggest that there are approximately 100 to 400 billion stars in the Milky Way, with significant uncertainties remaining due to the difficulty in detecting faint red dwarfs and brown dwarfs."
      },
      "delta": {
        "role": "assistant",
        "content": ""
      }
    }
  ],
  "usage": {
    "prompt_tokens": 14,
    "completion_tokens": 70,
    "total_tokens": 84
  }
}

https://docs.perplexity.ai/api-reference/chat-completions