Add a systemd service definition for managing the coaching platform containers start/stop/restart

[jhodapp]

Description

This PR adds a systemd service definition for managing the coaching platform starting/stopping/restarting backend and frontend containers.

Currently, it needs to be manually copied over and installed onto the production server. Once in place, it shouldn't need to be reinstalled unless we have a new version of refactor-platform.service.

GitHub Issue: Closes #133

Changes

• Add a systemd service definition for managing the coaching platform containers starting/stopping/restarting
• Remove outdated docs/runbooks/deploy.md runbook and replace with relevant instructions covering systemd service management

Testing Strategy

1. Try starting the containers using systemctl as the deploy user, like so: systemctl start refactor-platform.service
2. Try stopping the containers using systemctl as the deploy user, like so: systemctl stop refactor-platform.service
3. Try restarting the containers using systemctl as the deploy user, like so: systemctl restart refactor-platform.service

Concerns

None

[jhodapp]

I'm going to leave this unmerged until we get a chance to try this out on the production server. I don't anticipate needing to make any changes, but it's a non-zero chance and we might as well do that in this PR.