[request] more granularity within MedicalAction.adverse_events

We may need more granularity within the immunological domain MedicalAction.adverse_events:
In here the severity of the adverse events may be helpful, e.g., Individual Y had a severe post-vaccine infection after HPV vaccination, but mild for yellow fever. Individual Z had a mild post-vaccine infection after Pneu-C-15 vaccine, but a severe Guillón Barré Syndrome after the Covid Vaccination.

Locate MedicalAction.adverse_events in the schema and review its current representation. Use the vaccine and adverse-event examples to clarify the required severity model, then confirm that the agreed schema change can represent different severities for each event.

Written by the indexing model from the issue text.