Reapply "feat(loyalty): EnakPoint & EnakCoin" (#32)

This reverts commit 4e24f9bbb0.

internal/contract/customer_device_contract.go

@@ -0,0 +1,11 @@
+package contract
+
+// RegisterCustomerDeviceRequest is PUT /customer/devices: the FCM token the customer
+// app got for this device. Send it after login and whenever FCM refreshes the token.
+type RegisterCustomerDeviceRequest struct {
+	DeviceID string `json:"device_id" binding:"required"`
+	FCMToken string `json:"fcm_token" binding:"required"`
+	// android, ios or web.
+	Platform   *string `json:"platform"`
+	AppVersion *string `json:"app_version"`
+}