ApiEndpoints Add support for IAsyncEnumerable

Right now, in order to return an IAsyncEnumerable you need to use EndpointBaseSync and access the request cancellationToken form HttpContext like this:

public class List : EndpointBaseSync.WithoutRequest.WithResult<IAsyncEnumerable<PropertyListResult>>
{
    /// <summary>
    /// List all Properties
    /// </summary>
    [HttpGet("api/[namespace]")]
    public override async IAsyncEnumerable<PropertyListResult> Handle()
    {
        var cancellationToken = HttpContext.RequestAborted;
        await Task.CompletedTask;
        yield break;
    }
}

It would be nice if we could do something like this:

public class List : EndpointBaseAsync.WithoutRequest.WithAsyncEnumerableResult<PropertyListResult>
{
    /// <summary>
    /// List all Properties
    /// </summary>
    [HttpGet("api/[namespace]")]
    public override async IAsyncEnumerable<PropertyListResult> Handle(CancellationToken cancellationToken = default)
    {
        await Task.CompletedTask;
        yield break;
    }
}