Add Coupon model for discount management

Author: namitha2526

app/models.py

@@ -100,4 +100,15 @@ class Supplier(Base):
     phone_number = Column(String, nullable=True)
     created_at = Column(DateTime(timezone=True), server_default=func.now())
     updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+class Coupon(Base):
+    __tablename__ = "coupons"
+    id = Column(Integer, primary_key=True, index=True)
+    code = Column(String, unique=True, index=True, nullable=False)
+    discount_percentage = Column(Integer, nullable=False)
+    valid_from = Column(DateTime(timezone=True), nullable=False)
+    valid_to = Column(DateTime(timezone=True), nullable=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+