Deploy bridgestrap on polyanthum

It's time to deploy a prototype of bridgestrap on polyanthum. Here's what we have to do:

• Create a separate user account for privilege separation. I filed an issue to have the user account "bridgestrap" created: tpo/tpa/team#40081 (closed)
• Deploy the bridgestrap binary and create a systemd script that starts it on boot.
• Create a monitoring target in our monit configuration (see tpo/tpa/team#40080 (closed)).
• Create a bridgestrap survival guide
• Consider logrotate for bridgestrap's log file.
• tpo/tpa/team#40094 (closed)