Previous refacto was creating output schema V2 which has more specific
schemas based on the step type. Before we were using one common schema,
which was too complex when searching for variable informations.
This PR migrate the deprecated schemas and remove the old code:
- mark previous `BaseOutputSchema` as deprecated
- remove other previous schemas
- use V2 everywhere
- icon should not be stored in schema. Instead it should be generated
based on the fieldmetadata or the item type
