add base_url to llmobs spans in open ai integration

[ncybul]

This PR modifies existing integrations for Open AI, Anthropic, [TODO] in order to capture the base_url parameter that is used to route requests made to these providers through a proxy like the one provided by LiteLLM.

A follow-up to this PR will be creating a standalone integration for the LiteLLM Python SDK which will be helpful for identifying when a request is being routed through LiteLLM. This will allow us to attach the ml-proxy:litellm tag to these requests.

Manual Testing (TODO: add code snippets and screenshots for testing out each integration)

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/contrib/internal/anthropic/patch.py                             @DataDog/ml-observability
ddtrace/llmobs/_constants.py                                            @DataDog/ml-observability
ddtrace/llmobs/_integrations/anthropic.py                               @DataDog/ml-observability
ddtrace/llmobs/_integrations/openai.py                                  @DataDog/ml-observability
ddtrace/llmobs/_llmobs.py                                               @DataDog/ml-observability

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-02-21 21:12:23

Comparing candidate commit fb6de58 in PR branch nicole-cybul/openai-integration-support-for-litellm with baseline commit 7011d3c in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 418 metrics, 2 unstable metrics.