Clean-up Open AI resource.

[mitchdenny]

We don't need an AddOpenAI extension method on the DAB. The reason is that when using the Open AI service we are not provisioning any resources, instead we can just use AddConnectionString(...) and punch in the API key for the Open AI API (e.g. Key=[key from https://platform.openai.com/api-keys].

This is distinct from AddAzureOpenAI which will ultimately result in a deployment and needs resource specific endpoints.

Also in this PR I've added a fairly simplistic app which uses the completions API to generate a story with a REALLy basic ux.

Microsoft Reviewers: Open in CodeFlow

[eerhardt]

Is it possible to use Parameters and ConnectionString together?

For example imagine I have:

var openaiKey = builder.AddParameter("OpenAIKey");

var openai = builder.AddConnectionString($"Key={openaiKey.Value}");

That way people wouldn't need to know about the connection string format. They would just stick the actual key into the parameter, and the above code would do the formatting for them.

[mitchdenny]

No that isn't possible at the moment. File an issue? There would need to be some consideration on how interpolation would work here because the "secretness" of one parameter would have to poison all the other parameters it was injected into (btw in this example you would want to use AddParameter("OpenAIKey", secret: true). Only AddConnectionString(...) defaults to being secret.