support PostgreSQL/openGauss default schema in ds config

[wy1433]

Fixes #17204.

Changes proposed in this pull request:

• support PostgreSQL/openGauss default schema in config-xxx.xml , Users can specify the search_path of PostgreSQL/openGauss by configuring currentSchema=schemaName
• Limit : only support config a single default schema now

---

Before committing this PR, I'm sure that I have checked the following options:

• My code follows the code of conduct of this project.
• I have self-reviewed the commit code.
• I have (or in comment I request) added corresponding labels for the pull request.
• I have passed maven check locally : ./mvnw clean install -B -T1C -Dmaven.javadoc.skip -Dmaven.jacoco.skip -e.
• I have made corresponding changes to the documentation.
• I have added corresponding unit tests for my changes.
• I have updated the Release Notes of the current development version. For more details, see Update Release Note