Scheduler Improvements

[mmstick]

• Fixes the config trying to load from /usr/lib/system76-scheduler/config.ron instead of the correct path of /usr/share/system76-scheduler/config.ron for configuring the background and foreground priorities.
• Uses tracing for logging of messages. Running sudo env RUST_LOG system76-scheduler daemon will have an instance with debug logs printed.
• Adds error messages for configuration files that failed to deserialize
• Makes it possible to have process assignments without automatic background and foreground adjustments
• Combines AutoBackgroundPriority events with the UpdateProcessMap event because both are generated at the same time.

Closes #9
Closes #12
Closes #14

[jacobgkau]

Adding this branch causes system76-scheduler to be kept back when running apt upgrade. This also causes an uninstallable update in the Pop!_Shop:

Since irqbalance is installed by default (recommended by ubuntu-standard) on current installations, we can't just conflict with it out of the blue, since apt won't remove a package via a normal upgrade. May need an empty transitional package or some other solution (or the irqbalance removal could be a 22.04 feature.)

[mmstick]

Sad. I'll remove the last commit then. Maybe it'd be best to make it a dummy package.

[jacobgkau]

Fixes config file loading; I can now change the default nice levels for foreground & background tasks using the file in /usr/share (although that file is part of the package and seems to be overwritten on upgrade, which is expected.)

Foreground changes are no longer logged to journalctl, as stated.

After setting foreground and background to None, manual assignments still take effect.

When running a command in a terminal (e.g. stress -c 1), it sometimes takes a few focus switches to get the command itself (instead of just the terminal GUI) to have a "focused" nice level, testing with Konsole (while watching top in GNOME Terminal). However, that is not a regression.