operations: automate restoration of backups from `prod` to `qa`

[GraemeWatt]

A method of easily restoring prod backups of the CephFS data directory and PostgreSQL database to qa should be developed, and maybe automatically run at regular intervals (daily/weekly). The qa Elasticsearch indices could maybe be recreated if this is easier than copying the corresponding prod indices to qa.

Originally posted by @GraemeWatt in https://github.com/HEPData/hepdata/issues/376#issue-936952110