Python: Fix OpenAI chat client compatibility with third-party endpoints and OTel 0.4.14#4161

eavanvalkenburg merged 5 commits intomicrosoft:mainmicrosoft/agent-framework:mainfrom

eavanvalkenburg:fix/1407-system-message-content-listeavanvalkenburg/agent-framework:fix/1407-system-message-content-listCopy head branch name to clipboard