fix(llm): delete unused request header when ai upstream provider is a…

[oowl]

…zure

Summary

due to the limitation of Azure documents, we need to delete unused header when ai-proxy use azure provider.
https://learn.microsoft.com/en-us/azure/ai-services/openai/quotas-limits

1 Our current APIs allow up to 10 custom headers, which are passed through the pipeline, and returned. Some customers now exceed this header count resulting in HTTP 431 errors. There's no solution for this error, other than to reduce header volume. In future API versions we will no longer pass through custom headers. We recommend customers not depend on custom headers in future system architectures.

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

https://konghq.atlassian.net/browse/AG-179