feat(battery): added support for battery state-based classes on the entire waybar

[ArneshRC]

The battery module now applies a single battery state-based class, .battery-<state> on the entire waybar.

This could be useful for, say, changing the bar's background color based on battery level.

config.jsonc:

"battery": {
    "states": {
        "warning": 30,
        "critical": 15
    },
}

style.css:

window#waybar.battery-warning {
  background-color: rgba(247, 218, 68, 0.2);
}

window#waybar.battery-critical {
  background-color: rgba(247, 68, 68, 0.2);
}

I'm sure there are quite a few users who would appreciate this feature: https://www.reddit.com/r/swaywm/comments/kuf9sm/make_waybar_turn_red_as_warning/

[Alexays]

LGTM, can you update the man and github wiki to show this new feature? :)

[ArneshRC]

Done! :)

[ArneshRC]

Made some small changes. As of d14a4a2, everything's working as expected.

[Alexays]

Thanks!