fix Decimal field serialization

Author: giancarloromeo

packages/models-library/src/models_library/api_schemas_resource_usage_tracker/pricing_plans.py

@@ -1,7 +1,8 @@
 from datetime import datetime
 from decimal import Decimal
+from typing import Annotated
 
-from pydantic import BaseModel, ConfigDict
+from pydantic import BaseModel, ConfigDict, PlainSerializer
 
 from ..resource_tracker import (
     HardwareInfo,
@@ -18,7 +19,7 @@ class PricingUnitGet(BaseModel):
     pricing_unit_id: PricingUnitId
     unit_name: str
     unit_extra_info: UnitExtraInfo
-    current_cost_per_unit: Decimal
+    current_cost_per_unit: Annotated[Decimal, PlainSerializer(float, return_type=float, when_used='json')]
     current_cost_per_unit_id: PricingUnitCostId
     default: bool
     specific_info: HardwareInfo

services/resource-usage-tracker/openapi.json

@@ -459,7 +459,7 @@
             "$ref": "#/components/schemas/UnitExtraInfo"
           },
           "current_cost_per_unit": {
-            "type": "string",
+            "type": "number",
             "title": "Current Cost Per Unit"
           },
           "current_cost_per_unit_id": {