feat(gold_standard): add traitFromSourceMappedId to schema

[ireneisdoomed]

✨ Context

This PR adds the EFO ID to the gold standard so that we can split the training set by EFO/Gene during cross validation.
The change in the schema doesnt have implication in FE/BE as discussed.
Bare in mind this will create some explosion in the gold standard.

🛠 What does this PR implement

🙈 Missing

A following PR will make more thorough changes in the schema of the gold standard, and in the code to accommodate this dataset to the definition of a effector gene list.
The new field is set to nullable = True for the time being, so that tests don't complain. This field should be mandatory in the future.

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[ireneisdoomed]

Feature matrix doesn't have a schema.
But I need to define that this column is expected as one of the fixed columns to pivot on.