v2.0.0

Bumb php version to 8.1. Update composer dependencies.

1. Refactor package with new features and structure. Rewrite storage logic.

2. Throw an exception when trying to render or handle step when previous one is not submitted.

3. Add step key validation.

4. Add isDynamic method to the FormBuilder.

5. Don't run forgetAfter if the form builder is static or step implements StepBehaviourInterface and its method returns false.

6. Remove access to Step object from exceptions. Add Step key instead of step.

7. Return step key on form methods instead of full step

8. Set current step only when renderable step is found.

9. Fixed forgetAfter method.

10. Fixed StepIsNotSubmittedException exception data.