feature request: do not make hdajackretask hard depend on systemd or provide the functionality for openrc/other init systems

alsa-project/alsa-tools issue #46 was opened from ingenarel:

currently, at the time of writing this, hdajackretask calls systemctl directly
https://github.com/alsa-project/alsa-tools/blob/d444519df40d52de3903513a14085a0619f688db/hdajackretask/apply-changes.c#L137

which makes it not work on non systemd systems, for example openrc, which i'm currently using

with systemd's recent controversies with age verification and everything, more and more users are trying out alternative init systems and using non systemd systems in a day to day basis, but hdajackretask does not work on that

for the fix, i have an idea:
hdajackretask could try to detect what init system is running, and it could then run the appropriate commands, if it's unable to detect the init system, or fail to run the commands, it could then open a prompt saying:

```
unable to (detect the init system OR run command OR basically wtv happend)
please run these commands or their equivalent manually
systemctl systemctlstuff
```

if hdajackretask needs to do more stuff afterwards, the prompt can just wait after the user clicks "done" or something, and then it could continue doing the rest of the stuff

if upstream decides to do this functionality, then they could also add the logic for openrc/other init systems or anything whenever they want, without breaking the rest of the stuff

Issue URL     : https://github.com/alsa-project/alsa-tools/issues/46
Repository URL: https://github.com/alsa-project/alsa-tools