Python: Azure OpenAI Chat sample assumes keyless RBAC and specific env variables

[e-straight]

Assumes keyless RBAC role is assigned and .env has AZURE_OPENAI_ENDPOINT and AZURE_OPENAI_CHAT_DEPLOYMENT_NAME

Sample: https://github.com/microsoft/agent-framework/tree/main/python/samples/getting_started/agents/azure_chat_client