Consider adding OpenAIClient ctor for AuthenticationPolicy and Uri

[stephentoub]

To use OpenAIClient (rather than AzureOpenAIClient) to connect to Azure OpenAI, you need to use an OpenAIClientOptions to set the endpoint, e.g.

OpenAIClient client = new(
    new BearerTokenPolicy(new AzureCliCredential(), "https://ai.azure.com/.default"),
    new OpenAIClientOptions()
    {
        Endpoint = new Uri(endpoint)
    };

It'd be a bit simpler if the Uri could just be passed to the constructor directly, e.g.

OpenAIClient client = new(
    new BearerTokenPolicy(new AzureCliCredential(), "https://ai.azure.com/.default"),
    new Uri(endpoint));

[jsquire]

@KrzysztofCwalina: This request falls under your governance. Your thoughts would be appreciated.

//cc: @christothes

[KrzysztofCwalina]

It would be slightly simpler, but it could be confusing to users of the OpenAI service, which does not need a user provided uri.
We in a process of designing support for configuration system for the library, at which point there won't be a need for passing the uri explicitly. In our prototype, the code looks like the following, and it configures not only the uri but also the model, credentials, etc:

ConfigurationManager configuration = new();
configuration.AddJsonFile("appsettings.json");
ChatClient chat = configuration.CreateChatCLient("ChatClient");