Fix the example of ntp server address

* 去除alter外键约束时ob_ddl_timeout的约束，修改遗失返回码和dead code的问题

* 修改log记录的信息，修改移除dead code的代码

Enable pch and unity option in compiling process of rpm mode in order to keep consistent with other modes.

[Essence Securities]fix occur error after transform subquery pullup when view not set parent namespace stmt.

* Added some documents synchronized from ICMS, deleted some documents that were not in the Oceanbase database community edition and added a folder junior-Training under the Docs folder to store some beginner learning documents.

* modify requirements.txt
Co-authored-by: Nzhijiuxing-alt <322676446@qq.com>