feat(payments): add discount code admin API

apps/payments/api/schemas.py

@@ -1,4 +1,42 @@
 from ninja import Schema
+from datetime import datetime
+
+
+class DiscountCodeSchema(Schema):
+    id: int
+    code: str
+    type: str
+    value: int
+    max_discount: int | None = None
+    is_active: bool
+    starts_at: datetime | None = None
+    ends_at: datetime | None = None
+    usage_limit_total: int | None = None
+    usage_limit_per_user: int | None = None
+    min_amount: int | None = None
+    applicable_event_ids: list[int]
+    usage_count: int = 0
+    created_at: datetime
+    updated_at: datetime
+
+
+class PagedDiscountCodeSchema(Schema):
+    count: int
+    results: list[DiscountCodeSchema]
+
+
+class DiscountCodeWriteSchema(Schema):
+    code: str
+    type: str = "percent"
+    value: int
+    max_discount: int | None = None
+    is_active: bool = True
+    starts_at: datetime | None = None
+    ends_at: datetime | None = None
+    usage_limit_total: int | None = None
+    usage_limit_per_user: int | None = None
+    min_amount: int | None = None
+    applicable_event_ids: list[int] = []
 
 
 class CreatePaymentIn(Schema):