쿠폰 생성 API 수정

AS-IS: 유효기간 타입 LocalDateTime
TO-BE: 유효기간 타입 String

src/main/kotlin/kr/co/vividnext/sodalive/can/coupon/GenerateCanCouponRequest.kt

@@ -1,12 +1,11 @@
 package kr.co.vividnext.sodalive.can.coupon
 
 import com.fasterxml.jackson.annotation.JsonProperty
-import java.time.LocalDateTime
 
 data class GenerateCanCouponRequest(
     @JsonProperty("couponName") val couponName: String,
     @JsonProperty("can") val can: Int,
-    @JsonProperty("validity") val validity: LocalDateTime,
+    @JsonProperty("validity") val validity: String,
     @JsonProperty("isMultipleUse") val isMultipleUse: Boolean,
     @JsonProperty("couponNumberCount") val couponNumberCount: Int
 )