Detect and prefer system-provided service

[Scrumplex]

Instead of always creating our own service file for the user, detect if
there is a service already present, and skip installing our own
service file.

Some distributions might choose to package the user service as well. For example the AUR packages take the template in the repo, replace the binary path and install it to /usr/lib/systemd/user/espanso.service. To keep the systemd environment of users of those packages clean, we should first check if a service already exists.

[Scrumplex]

Rebased on dev instead

[federico-terzi]

Hey @Scrumplex ,

Thank you for the help! This is super helpful! Please bear with me for delays in the review, I'm going through the busiest period of my life and I only have limited capacity for OS at the moment. I'll get back to you as soon as I can, I hope you'll understand :)

Cheers :)

[federico-terzi]

Hey!
I've got the chance to review the PR, thank you for the help!
Perhaps I'm missing something, but I don't fully understand the use-case for this additional check. If the service file is installed by the package manager (such as with the AUR package), the start command should be able to pick it up correctly and not require the register command. Just to make sure that I understand, you're suggesting to add this check because a user might:

• Install Espanso through the AUR
• Run espanso service register (even though it's not needed there) and misconfigure the service

Did I understand correctly?

Cheers :)

[Scrumplex]

Rebased on dev.

So the problem is the following: On a fresh installation of the AUR package, the service file will be installed for all user environments, but will be disabled by default. Now, if I try to run espanso start, it will tell me that the service is not registered. So the user will just do what espanso says and run espanso service register, which will then place a new systemd unit in the user's folder.
As we already shipped one as part of the package, we only really want to enable the existing unit.
So this PR just adds a check to avoid creating a duplicate systemd unit.

[Scrumplex]

By the way: I kinda forgot about this PR 👀

[AucaCoyan]

Hi! I believe this changes are still relevant to the date
Is it possible to merge this PR?