Add Initializer interface empty markup

[aochmann]

Use case:

public interface IAzureInitializer
{
}

public interface IAzureInitializer<in TAzureModel> : IAzureInitializer where TAzureModel : class, IAzureModel, new()
{
        Task<AzureIndexOperationResult> InitializeAsync();
}

//...

public class SomeStartupService
{
    private readonly IEnumerable<IAzureInitializer> _initializers;

    public SomeStartupService(IEnumerable<IAzureInitializer> initializers)
      => _initializers = initializers;

   public async Task InitializeAll()
   {
        foreach(var initializer in _initializers)
        {
             _ = await initializer.InitializeAsync();
        }
   }
}