Adds helper overload of AddAzureAppConfiguration for using EntraId (token credential)

[Krzysztof Cwalina (KrzysztofCwalina)]

fixes #693

It's now possible to do:

builder.AddAzureAppConfiguration(endpoint, credentials);

instead of, less discoverable,:

builder.AddAzureAppConfiguration(options => {
    options.Connect(endpoint, credentials);
});

[Avani Gupta (avanigupta)]

Krzysztof Cwalina (@KrzysztofCwalina) looks like Zhiyuan Liang (@zhiyuanliang-ms) also created the same PR here: #694
Which one of you would like to continue? :)

[Krzysztof Cwalina (KrzysztofCwalina)]

I am going to close this one, if you guys have your own. Thanks you!!!