refactor(models): make customer_id and appointment_date optional fields

Change customer_id and appointment_date from required to optional fields to accommodate cases where these values may not be available at creation time

app/models/appointment.py

@@ -51,8 +51,8 @@ class Appointment(BaseModel):
     city: str = Field(..., description="City is required")  # ✅ Mandatory
     merchant_address: Dict[str, Any] = Field(..., description="Merchant address is required")  # ✅ Mandatory
     location_id: str
-    customer_id: str = Field(..., description="Customer ID is required")  # ✅ Mandatory
-    appointment_date: date = Field(..., description="Appointment date (YYYY-MM-DD)")  
+    customer_id: Optional[str] = Field(None, description="Customer ID is optional")  # ✅ Optional
+    appointment_date: Optional[date] = Field(None, description="Appointment date (YYYY-MM-DD)")
     appointment_time: str = Field(..., pattern=r"^\d{2}:\d{2}$", description="Appointment time in HH:MM format")
     associates: List[AssociateDetails]  # ✅ Using `AssociateDetails` model
     status: AppointmentStatus  # ✅ Using Enum