Add invite user feature for admin

internal/dto/in.go

@@ -70,3 +70,7 @@ type UserSignup struct {
 	Username string `json:"username" binding:"required,min=2,max=20"`
 	Password string `json:"password" binding:"required,min=6,max=100"`
 }
+
+type UserToInvite struct {
+	Username string `json:"username" binding:"required,min=2,max=20"`
+}