Overwrite the config paramters for a step in PPP run

[project-defiant]

Context

The addition of OTAR2081 dataset to the evidence parsers allows us to add a new source of annotation to the variantIndex generation step in gentropy configuration.

This dataset annotations should be only available for the PPP release. This means that we neeed to add a way to overwrite the variant_index step with additional parameters for PPP only run.

@DSuveges @javfg

[javfg]

There is something like that already:

https://github.com/opentargets/orchestration/blob/dev/src/ot_orchestration/dags/config/unified_pipeline.py#L119

Which adds steps to the DAG conditionally depending on whether the run is standard or PPP.

What we need to do is something similar that allows us to extend the gentropy config with a params_ppp that get appended only if the run is_ppp.

That way you avoid coupling the paramaters of Gentropy steps into the orchestrator config.