Support for extra_body parameter for embeddings API

[AyushSawant18588]

Describe the change
This change adds support for an ExtraBody parameter in the EmbeddingRequest struct, allowing developers to include additional, arbitrary key-value pairs in the API request payload. This ensures extensibility and flexibility when working with the OpenAI Embeddings API, especially for experimental features, future API updates, or custom parameters that are not explicitly defined in the current request structure. The addition of ExtraBody is particularly valuable for supporting LLM engines like vLLM, Nvidia NIM, etc, which may require additional fields beyond the standard parameters. Refrence
There is an issue created that ExtraBody parameter support is required for vLLM engine also. #898
In this PR ExtraBody parameter support is added only for embedding API but it can be extended for other APIs as well like chat completions

Provide OpenAI documentation link
OpenAI's official python client also supports this extra_body field which this go client could also support. Refrence

Describe your solution
The solution involves:
Introducing the ExtraBody field in the EmbeddingRequest struct. This is a map of string keys to arbitrary values (map[string]any) that allows developers to pass additional fields to the API dynamically.
Updating the CreateEmbeddings method to merge the ExtraBody values into the main request payload (body) before sending it to the API. This is done through the withExtraBody request option, which ensures the fields in ExtraBody are included without overwriting existing mandatory parameters.

Tests
Added unit tests and done sanity check of embeddings api with extra_body param for Nvidia NIM embedding model

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.71%. Comparing base (774fc9d) to head (bc7a940).
Report is 77 commits behind head on master.

Additional details and impacted files

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+ Coverage   98.46%   98.71%   +0.25%     
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  Files          24       26       +2     
  Lines        1364     1789     +425     
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+ Hits         1343     1766     +423     
- Misses         15       16       +1     
- Partials        6        7       +1     

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[AyushSawant18588]

@sashabaranov Can you please look into this?

[AyushSawant18588]

@sashabaranov Can you please look into this PR? thanks

[gavrissh]

@sashabaranov Would require your assistance in getting these changes in. Thank you

[nagar-ajay]

@sashabaranov can you please check this? Thanks!

[sashabaranov]

@AyushSawant18588 Thank you for updating the PR! I'm re-reading it for the fifth time, and there's something odd about it—and I can't pinpoint what it is exactly. It feels like we're adding a lot of counterintuitive logic for a tiny use case.

If the goal is to add {"input_type": "query", "truncate": "NONE"} to Embedding requests, maybe that's literally what we should do — just add two fields to EmbeddingRequest. Or are there more use cases I don't know of?

[AyushSawant18588]

@sashabaranov So the official OpenAI Python client offers an extra_body field for all inference APIs. For example, in the embedding API implementation, you can see this feature being used here: Embeddings API. Their implementation and behaviour is same as done in this PR.
The extra_body parameter allows users to add arbitrary JSON properties to the request body. This approach is particularly useful when working with diverse LLM engines that may introduce additional or custom fields in their APIs. Instead of updating the struct for every unique field, this mechanism provides flexibility to include extra fields as needed without modifying the core structure repeatedly.
Here are some examples where extra parameters may vary depending on the API and LLM engine:

• https://docs.vllm.ai/en/latest/serving/openai_compatible_server.html?ref=blog.mozilla.ai#extra-parameters
• https://build.nvidia.com/nvidia/nv-embedqa-e5-v5?snippet_tab=Python
• https://github.com/openai/openai-cookbook/blob/f689f7d963d97b930dfce8645a9decd8e7a526ba/examples/azure/chat_with_your_own_data.ipynb#L233

There is an issue created that ExtraBody parameter support is required for Completions API as well for vLLM engine. #898
This same structure can be used there as well.

[johnugeorge]

@sashabaranov

1. We see that all embedding servers including vLLM, Nvidia NIM support "extra_body" in the embedding request.
2. ExtraBody is supported in official OpenAI Python clients.
3. "input_type": "query", "truncate": "NONE" cannot be added to the embedding request as it will break OpenAI compatible server implementations(it is not compatible with OpenAI API standard)

Can you please look into this?

[lilien1010]

@sashabaranov Help!