externalize workspace buttons

[quantenzitrone]

First of all, thanks for making this, it is amazing, and I love to be able to use my i3status-rs config outside of sway.

I'm not sure, but I think all, the workspace button logic can be done through the i3bar protocol. So one simple approach would be making the same i3bar protocol we have on the right also for the left. To make this work, we would also need to create such a workspace button generator for river and hyprland. Maybe i3status-rs will add workspace modules once this works.