title: AddSingleton with async Invoke?
body: <p>I add a singleton like this.</p>
  <p>In Startup.cs, I add the following:</p>
  <pre><code>services.AddSingleton&lt;MySingleton&gt;();
  </code></pre>
  <p>I want to build my singleton like this (which is not possible of course):</p>
  <pre><code>public class MySingleton
  {
      public MySingleton()
      {
          await InitAsync();
      }
  
      private async Task InitAsync()
      {
          await Stuff();
      }
  }
  </code></pre>
  <p>How can I solve this problem without creating deadlocks?</p>