[BE] fix: 현재 사용자도 DirectMember에 추가 (#92)

Author: toychip

src/backend/guild-server/src/main/java/com/asyncgate/guild_server/service/DirectServiceImpl.java

@@ -30,7 +30,10 @@ public class DirectServiceImpl implements DirectService {
     @Override
     @Transactional
     public DirectResponse create(final String currentUserId, final DirectChannelCreateRequest request) {
-        List<String> memberIds = request.getMemberIds();
+        List<String> memberIds = new ArrayList<>(request.getMemberIds());
+        if (!memberIds.contains(currentUserId)) {
+            memberIds.add(currentUserId);
+        }
 
         UserClientInfoResponses usersInfo = userClient
                 .getUsersInfo(memberIds)