Alternative to systemd services

[Jacalz]

While I personally have systemd on my Linux systems, we might want to look at an option to not use it for those that wish to do so. I think this also would be important for getting fin running on FreeBSD and OpenBSD as well. This requires more research for other init systems and how their services work and so on before we commit to anything though.

[Jacalz]

This seems to be the best documentation that I have found in the FreeBSD unit system: https://docs.freebsd.org/en/articles/rc-scripting/#rcng-daemon

The init section here is also quite well detailed: https://unixsheikh.com/articles/technical-reasons-to-choose-freebsd-over-linux.html

They seem to be using BSD init or init.d. We probably also want to support OpenRC and maybe runit, but BSD init and OpenRC seems to be the two most prominent init systems. From what I can tell, only Void Linux use runit.