feat(github-copilot): Add Embedding API support

[codgician]

Title

Adds Embedding API support for GitHub Copilot's embedding models. According to the GitHub Copilot API, you can specify model ID as:

• text-embedding-ada-002
• text-embedding-3-small
• text-embedding-3-small-inference

(They seem to have the same underlying model anyway).

I'm new to this project and the coding work is aided by AI. Please let me know if the current implementation fits the coding standard.

Relevant issues

Fixes #13564

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement - see details
• I have added a screenshot of my new test passing locally
• My PR passes all unit tests on make test-unit
• My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🆕 New Feature

Changes

Added support for GitHub Copilot Embeddings API. The implementation:

• Created GithubCopilotEmbeddingConfig to handle embedding requests for models like text-embedding-ada-002 and text-embedding-3-small.
• Fixed a routing precedence issue in main.py to ensure custom_llm_provider="github_copilot" is respected even for known OpenAI model names.
• Implemented automatic list wrapping for string inputs to match API requirements.
• Reused existing OAuth authenticator for seamless integration.
• Extracted some common constants and copilot default headers into common_utils.py, so it could be shared for different model implementations for GitHub Copilot.

A working LiteLLM proxy configuration:

model_list:
- model_name: text-embedding-ada-002
  model_info:
    mode: embedding
  litellm_params:
    extra_headers:
      editor-plugin-version: copilot/1.388.0
      editor-version: vscode/1.106.2
    model: github_copilot/text-embedding-ada-002
- model_name: text-embedding-3-small
  model_info:
    mode: embedding
  litellm_params:
    extra_headers:
      editor-plugin-version: copilot/1.388.0
      editor-version: vscode/1.106.2
    model: github_copilot/text-embedding-3-small
- model_name: text-embedding-3-small-inference
  model_info:
    mode: embedding
  litellm_params:
    extra_headers:
      editor-plugin-version: copilot/1.388.0
      editor-version: vscode/1.106.2
    model: github_copilot/text-embedding-3-small-inference

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[codgician]

The failing test tests/test_litellm/llms/bedrock/test_anthropic_beta_support.py is unrelated to this change and fails without this commit.

[ghost]

@codgician this looks good to me. can you file a follow up PR to document embedding api support on here -

litellm/docs/my-website/docs/providers/github_copilot.md

Line 4 in 01dfc35

# GitHub Copilot

?

This will allow others to know this exists as well

[codgician]

@codgician this looks good to me. can you file a follow up PR to document embedding api support on here -

litellm/docs/my-website/docs/providers/github_copilot.md

Line 4 in 01dfc35

# GitHub Copilot

?

This will allow others to know this exists as well

Sure, I'll look into it this week.