Hyprland workspaces hosting-monitor css class

[jramrath]

Adds the css class onThisMonitor.
This will make it possible to only style the waybar that a workspace is on.

Example:

#workspaces .onThisMonitor {
  color:blue;
}

/* waybar of monitor 1 with workspace A open:   [    A       B    ]
 *                                                  blue   white
 *
 * waybar of monitor 2 with workspace B open:   [    A       B    ]
 *                                                 white    blue
 */

Closes #2959

[jramrath]

Sorry for the wait.
I went with hosting-monitor for the css class name.

[Alexays]

LGTM, thx!
Can you also add the new option to the github wiki?