[Improvement-12658][Permission] Improve the readability of setPerm() in grantProjectbyCode() (#12660)

dolphinscheduler-api/src/main/java/org/apache/dolphinscheduler/api/service/impl/UsersServiceImpl.java

@@ -722,7 +722,7 @@ public class UsersServiceImpl extends BaseServiceImpl implements UsersService {
             projectUser = new ProjectUser();
             projectUser.setUserId(userId);
             projectUser.setProjectId(project.getId());
-            projectUser.setPerm(7);
+            projectUser.setPerm(Constants.AUTHORIZE_WRITABLE_PERM);
             projectUser.setCreateTime(today);
             projectUser.setUpdateTime(today);
             this.projectUserMapper.insert(projectUser);