support postgresql version 15

[zhongjiajie]

In #12 we pin pg version to 15, we can not support postgresql 15 and will raise error running command bash "${DOLPHINSCHEDULER_HOME}/tools/bin/upgrade-schema.sh".

and pg-15 release in 2022-11-13 https://www.postgresql.org/about/news/postgresql-15-released-2526/, we should better support it later