Azure-functions-durable-extension: Enable DI support for class-based entities

[cecilphillip]

Description

Would love to see class based Durable Entities work with the built-in dependency injection support for Functions. Looks like it was mentioned in #763, I don’t think the feature was enabled.

Example

I’m guessing the programming model would look similar to how DI works with non-Durable Functions today.

public class Counter
{
    [JsonProperty("value")]
    public int CurrentValue { get; set; }
    public int Get() => this.CurrentValue;

    private ILogger _logger;
    private IMyService _service;

    public Counter(ILogger logger, IMyService service) {
         _logger = logger; 
         _service = service; 
   }
    [FunctionName(nameof(Counter))]
    public static Task Run([EntityTrigger] IDurableEntityContext ctx)
        => ctx.DispatchAsync<Counter>();
}

[cgillum]

@ConnorMcMahon I think this would be a good one for you to investigate. I think it's going to be really important to enable something like this in order for Durable Entities to become viable for production applications. There might be two angles to consider:

1. Could we accomplish what Cecil mentioned above? Basically, allowing users to declare what interfaces they want in the entity class constructor.
2. (Possibly related) Could users call ctx.DispatchAsync<ICounter>() and then get the implementation of ICounter from DI? I haven't figured out exactly what scenarios this would enable, so it might be worth considering possible use-cases first.

Fabio might be able to provide some guidance on how we can achieve this, if necessary.

[cgillum]

This has been merged and will be part of the v2.0.0-beta2 release.