feat: add Servam AI LLM integration with OpenAI-like interface

[Yash-1511]

Description

Summary of the Change:

This PR adds support for the Sarvam AI model provider to LlamaIndex. This includes implementation of the provider interface, configuration setup, and documentation for easy integration by users.

Fixes: # None

Motivation and Context:

The addition of Sarvam AI expands the range of available model providers in LlamaIndex, giving users more flexibility and potentially better performance or cost options depending on their needs. This aligns with the goal of making LlamaIndex a flexible and extensible framework for large language model applications.

https://docs.sarvam.ai/api-reference-docs/chat/completions
https://servam.ai

Dependencies:

• No new external dependencies introduced.
• Only requires appropriate API access for Sarvam AI.

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New Package?

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• No

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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How Has This Been Tested?

• I added new unit tests to cover this change
• I believe this change is already covered by existing unit tests

Tested both programmatically and via sample notebook integrations to ensure Sarvam AI responds as expected and integrates well into the llama-index ecosystem.

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Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran uv run make format; uv run make lint to appease the lint gods