investigate Postgres QA DB with limited read/write access

[sybenzvi]

This ticket is inspired by an online discussion with @sbailey. The existing SQLite history QA DB should automatically protects against accidental writes during testing by the non-desi (datasystems) user at NERSC (KPNO). However, by experience SQLite's lock file mechanism can lead to unpredictable race conditions when the DB is accessed by multiple processes, potentially corrupting the database.

PostgreSQL is friendlier to multi-process access but needs to be configured to allow read/write access only to the desi (datasystems) user. It should be read-only for all other users.