postgresql和greenplum 无法获取schema

### Before asking

- [X] I have read the [How to ask for help](https://linkis.apache.org/community/how-to-ask-for-help) (我已阅读[如何寻求帮助](https://linkis.apache.org/zh-CN/community/how-to-ask-for-help)指引文档).

### Your environment

- Linkis version used: 1.4.0
- Exchangis version used: 1.1.2
- Environment name and version:
- greenplum-9.4.24
- scala-2.12.2
- jdk 1.8.0_121

### Describe your questions

Exchangis中数据类型为postgresql 选择 database后无法展示schema，是因为Linkis的 org.apache.linkis.metadata.query.service.postgres.SqlConnection 中 没有获取schema的方法