Summary:
adding automatic_ddl_mode arg to ybadmin create_xcluster_checkpoint
Jira: DB-14500

Test Plan:
```
ybd --cxx-test xcluster_db_scoped-test --gtest_filter "XClusterDBScopedTest.TestYbAdmin"
```

Reviewers: hsunder, xCluster

Reviewed By: hsunder

Subscribers: ybase

Differential Revision: https://phorge.dev.yugabyte.com/D40690