Systemd support

[jfhbrook]

Now that dbus is being implemented (via #19), I'd like a dbus-activated systemd unit.

I believe that the current behavior of plusdeckd is sufficient for use with Type=dbus, but the docs may be worth going over.

https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html

Given I have such a unit, it would be cool to have a COPR package which includes the unit, which depends on python-plusdeck.

[jfhbrook]

Here's a prototype service file:

[Unit]
Description=Plus Deck 2C PC Cassette Deck

[Service]
Type=dbus
BusName=org.jfhbrook.plusdeck
ExecStart=/usr/bin/plusdeckd
Restart=on-failure

I believe I can install this to /usr/lib/systemd/system/plusdeck.service and then use systemctl enable plusdeck to manage that appropriately.

[jfhbrook]

Initial service file created, packaged, etc., in #29. Next up, testing.

[jfhbrook]

josh in 🌐 stardeck in stardeck on  main [!⇡] took 3m41s 
❯ sudo systemctl enable plusdeck
Failed to enable unit: Unit plusdeck.service does not exist

Guessing I need to put the systemd unit in another directory... hm.

[jfhbrook]

I ran into some lingering issues in #29, but decided to move forward with what I have and create a follow-up in #31. In addition, the release is stuck due to a COPR outage - see #34. But either way, calling this one sorted.