[#69995468]Add python packages needed by duplicity

Duplicity needs paramiko and gio to do backups to files or scp/sftp
[#69995468] Make the target scp and namespaced.

Make the default target more like what we would set for production.
Also make the per job target namespaced to the username
[#69995468] Encrypt the backups.

Use the GOV.UK Backup public key to encrypt the backups.