Add support for GaussDB database

[Tyhoning]

Add support for GaussDB database ,Thanks for you reviews.

[wgzhao]

Thanks your PR.

In my opinion, the OpenGauss database is compatible with PostgreSQL. Therefore, it can utilize PostgreSQL-related plugins to read from and write to the OpenGauss database. Even using the rdbmsreader and rdbmswriter plugins should achieve this goal.

[Tyhoning]

Thank you very much for your reply !
In fact, there are already many differences between GaussDB and PostgreSQL, such as ports, dialects, and some dependencies. In the future, there will be even more differences. This submission allows GaussDB to be used more smoothly without having to consider compatibility issues with other databases. The same applies if new features, such as the upsert function, are added in future versions.