eli-579 initialising the AddDaysHandler in the registry on app start

Author: eddalmond1

src/eligibility_signposting_api/services/processors/derived_values/__init__.py

@@ -0,0 +1,28 @@
+from eligibility_signposting_api.services.processors.derived_values.add_days_handler import AddDaysHandler
+from eligibility_signposting_api.services.processors.derived_values.base import (
+    DerivedValueContext,
+    DerivedValueHandler,
+)
+from eligibility_signposting_api.services.processors.derived_values.registry import (
+    DerivedValueRegistry,
+    get_registry,
+)
+
+__all__ = [
+    "AddDaysHandler",
+    "DerivedValueContext",
+    "DerivedValueHandler",
+    "DerivedValueRegistry",
+    "get_registry",
+]
+
+# Register default handlers
+DerivedValueRegistry.register_default(
+    AddDaysHandler(
+        default_days=91,
+        vaccine_type_days={
+            "COVID": 91,  # 91 days between COVID vaccinations
+            # Add other vaccine-specific configurations here as needed.
+        },
+    )
+)