OneFlow: multilevel user inputs

[MiguelERuiz]

Description
One feature it is desirable to maintain the variable definition from custom attributes, so despite of the fact custom_attributes is deleted on #6679, this feature is taken on user_inputs property from oneflow-template.

Besides, not only user_inputs can be defined at rol level but also at service level. With this, we get the following advantages:

• The possibility to create variables at rol scope
• The possibility to create variables at service level, that could be overwritten at rol level.
• A better control on the attributes of each rol (i.e expansion avoiding)

Use case
This feature should be useful on VRouters OneFlow declaration since we can declare variables at service scope that could be applied only for VRouters.

Interface Changes
Describe any changes you'd like to see to current interfaces including Sunstone, CLI, or/and API

Sunstone, Fireedge, CLI and OneFlow API.

Progress Status

• Code committed
• Testing - QA
• Documentation (Release notes - resolved issues, compatibility, known issues)