Implement Azure AI endpoints

[thekid]

These differ in the way they pass the API key and that they need an API version:

- use com\openai\rest\OpenAIEndpoint;
+ use com\openai\rest\AzureAIEndpoint;

- new OpenAIEndpoint('https://APIKEY@api.openai.com/v1');
+ new AzureAIEndpoint('https://APIKEY@example.openai.azure.com/openai/deployments/gpt-4-mini', '2024-02-01');

Otherwise, the code is the same.