Make able to set order for IConfigureOptions and IPostConfigureOptions

[VladyslavLishchyna]

Hi community, currently dotnet have mechanism for create and configurate options. Interfaces IConfigureOptions<> and IPostConfigureOptions<> is a part of this mechanism and this is really handy. Here in OptionsFactory all implementations of IConfigureOptions<> and IPostConfigureOptions<> are getting from dependency injection and invoke to configure options one by one.

Possible situation when some options class have few configurators and in this case order can be a key, but now we haven`t mechanism to manage order of this pipeline.

What I think about it.

My 1 thought:

Maybe good design is have single configuration class for each option and manage all action for configuration in this class (include order of actions). It`s helpful but we cant be sure that someone will not register additional configurator to DI and don't have not obvious side effect.

My 2 thought:

Maybe will be good to have in dotnet some general attribute that can show that some class object can have order and make possible to manage this order from code. Like example:

[AttributeUsage(AttributeTargets.Class)]
public class OrderAttribute(int order): Attribute
{
  public readonly int Order = order;
}

and then we can add it to IConfigureOptions<> and IPostConfigureOptions<> implementations like this:

[Order(5)]
public class Implementation : IConfigureOptions<SerilogOptions>
{
  public void Configure(SerilogOptions options)
  {
    throw new NotImplementedException();
  }
}

Nice here is that this change don't broke backward capability and this feature are as additional option (you can use it or not). In OptionsFactory possible set order as 0 for implementations that don't have this attribute.

So if you think that 2 thought are helpful, I can make pull request for it.