janus: Handle upgrades to 1.0.*

• Convert action to privileged
• Handle upgrades to 1.0.*
• upgrades: Hold janus during dist-upgrade

Tests:

1. Install Janus on stable system.
2. Start a dist-upgrade to testing.
   • Janus is held during dist-upgrade.
   • Janus is force upgraded by Plinth after dist-upgrade is complete.

Closes: #2254 (closed).

Signed-off-by: James Valleroy jvalleroy@mailbox.org