Docs improvement: Add page describing how to add attributes

[WhitWaldo]

I might recommend this be placed in a new page under "Advising code" in the conceptual documentation and organized like the "Adding initializers" page (assuming there's a non-programmatic way to do it).

While trying to work my way through doing it myself, I correctly guessed that I could get an IConstructor from an INamedType, but given that this requires a cast from the TypeFactory to an INamedType, this might not be the most obvious to someone new to the framework. For example, there's a lot here that takes some familiarity with Metalama to piece together what it's talking about:

var attr = AttributeConstruction.Create(
            myAttr.Constructor,
            new List<TypedConstant>
            {
                TypedConstant.Default(typeof(int)),
                TypedConstant.Default(typeof(int))
            },
            new List<KeyValuePair<string, TypedConstant>>());

And then one need to know how to actually attach that to the target, needing to know that they use the AddAttribute() method in the I*Builder while introducing the type.
'
I might recommend including a link to the aspect ordering page as a reminder that if they attach another aspect, they'll need to factor in ordering somewhere.

This would at least simplify understanding of some of the more advanced Metalama functionality.

[gfraiteur]

Done. https://doc.metalama.net/conceptual/aspects/advising/attributes