Add InviteLinkDTO + add dto folder

Co-authored-by: [Mahgs] <maxoerter@gmx.de>
Co-authored-by: Christoph <tobi@urpost.de>

src/main/java/mops/gruppen2/domain/dto/InviteLinkDTO.java

@@ -0,0 +1,13 @@
+package mops.gruppen2.domain.dto;
+
+import lombok.Data;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.relational.core.mapping.Table;
+
+@Table("invite")
+@Data
+public class InviteLinkDTO {
+    @Id
+    private Long group_id;
+    private String invite_link;
+}