[Docs] Adds possible implementation of invocable class to documentation

[tesar-tech]

Reasoning behind this change is to provide working example of invocable class.

The "closest" one in the docs is few lines below (invocable with params), where is "do not register them with the DI services.". Which is directly opposing the necessity with "normal" invokable.

For the better explanation user have to navigate to Invocables page.

This update keeps the full working example in one place.