Use the new Tails Persistent Storage copy option where applicable

[nathandyer]

Status

Ready for review

Description of Changes

This modifies the workflow in a couple key areas to use the new option in the Tails Installer that can copy an existing drive's Persistent Storage during a cloning operation.

It's worth noting that I elected not to use this tool for the backup procedures, instead preferring the current rsync based approach. This is because the current process allows for multiple workstation backups onto a single drive, which the Tails Installer tool does not allow. For that same reason, I have left the previous steps in place regarding the use of securedrop-admin backup and restore.

The second commit here changes the workflow for making a remote Secure Viewing Station. It does eliminate the use the "primary" USB drive, opting instead to clone the current SVS entirely (from an airgapped system). With this being a change in procedure with security implications, it may not be one we feel comfortable making; if not, I'm happy to remove that commit.

I will also note that I captured screenshots of the new Tails Installer, but did not feel it added to the documentation, so I elected to leave them out. If we believe it's worth including them, I can do so relatively easily.

• Resolves #491

Testing

• [x] CI passes
• [ ] Visual review

Checklist (Optional)

• [x] Doc linting (make docs-lint) passed locally
• [ ] Doc link linting (make docs-linkcheck) passed
• [x] You have previewed (make docs) docs at http://localhost:8000