Use azure-identity to log into Azure. (#13)

* Use azure-identity to log into the Azure instance instead of the key.

* Use azure-identity to log into the Azure instance - add 2 new model types to keep the original functionality.

* Revert "Use azure-identity to log into the Azure instance - add 2 new model types to keep the original functionality."

This reverts commit 5577231.

* Use azure-identity to log into the Azure instance - use env variable to control the type of identity used in Azure OpenAI.

* Update README.md

Co-authored-by: Marek Šuppa <mrshu@users.noreply.github.com>

* Reformatted to make black happy.

---------

Co-authored-by: David Strupl <dstrupl@gmail.com>
Co-authored-by: Marek Šuppa <mrshu@users.noreply.github.com>

README.md

@@ -47,6 +47,8 @@ If you use PyCharm, consider storing these in your
   OpenAI APIs.
 - `AZURE_OPENAI_API_KEY` and `AZURE_OPENAI_API_BASE`: Optional. Only if you want to use OpenAI
   models (ChatGPT, GPT-4, etc.) via Azure OpenAI APIs.
+  - `AZURE_OPENAI_USE_DEFAULT_CREDENTIALS`: Optional. If set to `True`, the Azure OpenAI API will use
+    the default credentials from the environment, as per https://learn.microsoft.com/en-us/python/api/overview/azure/identity-readme?view=azure-python
 - `PROMPTERATOR_DATA_DIR`: Optional. Where to store the files with your prompts and generated
   texts. Defaults to `~/prompterator-data`. If you plan to work on prompts for different tasks
   or datasets, it's a good idea to use a separate directory for each one.