Add functionality to load test dataset during staging setup

[zenmonkeykstop]

Description

To facilitate manual testing, it would be useful to be able to load a predefined dataset as part of the staging environment setup, for rationales similar to those in #5139. Another advantage of having this functionality in staging would be the ability to stand up both a workstation and staging server environment in Qubes, to allow for full testing of the workstation without additional hardware.

User Research Evidence

None, personal experience only

User Stories

As a QA tester, I want to be able to set up a staging environment with a reproducible state, to facilitate general and workstation manual tests.