Add "api-key" HTTP request header when using AzureKeyCredential

[dargilco]

• Some services require "Authorization: Bearer my-key", other require "api-key: my-key", when using API key authentication. To make client construction similar for these services, generate both HTTP request headers.
• Switch to using pip install azure-ai-inference[opentelemetry] instead of pip install azure-ai-inference[trace], to be more specific.
• Use vanity link to point to the AOAI table that shows their api-version (https://aka.ms/azsdk/azure-ai-inference/azure-openai-api-versions)
• For some reason the gpt-4o model in the AOAI deployment I was using for testing no longer responds. I'll need to look into it, but for now switch to using a different gpt-4o deployment (minor updates in test code).

[azure-sdk]

API change check

API changes are not detected in this pull request.