Fix the unconventional dbus names in the single instance plugin

[mrquantumoff]

Flathub no longer allows the "org.app_id.SingleInstance" dbus id that was allowed as an exception previously. Thus, I implemented an optional feature that would allow developers to use a more conventional dbus name that would pass the Flathub inspections without causing extra issues.

The Flathub discussion
flathub-infra/flatpak-builder-lint#819 (comment)

[FabianLars]

I really appreciate the PR but please check out #3184, we've had a slightly different approach in mind.

[mrquantumoff]

Thank you for informing me about your approach to this issue. I suppose your way of solving the problem is better than just adding an another feature to the crate. In this case, I'll wait for the official implementation and use my own implementation for the time being.

[FabianLars]

nono your implementation wasn't that far off. I just wouldn't put it behind a feature flag and instead force the new ids on all users 🤷

[FabianLars]

one thing that's a bit of an annoyance with zbus is the interface name, i'd like to have that match the dbus name but it needs to be defined at build time if we don't want to code everything ourselves. The spec says "should ..." when it comes to that though so ig it doesn't matter that much

[mrquantumoff]

In that case, I'll rework some part of it, to match the intended vision a bit more

[mrquantumoff]

I added an option to set the DBus ID at compile time. Made the conventional dbus naming the standard one. I chose to check for DBUS_ID instead of FLATPAK_ID in order to keep better compatability with people who want to package snaps.