Auto resize notification to width of output

Dunst has a neat feature where, if you specify a width greater than the screen a notification is show on, it will automatically resize it to the width of the screen. Quoting from `dunst(5)`:

> When setting a width bigger than the screen, dunst will clamp the width to the screen width. So if you want the notifcation to stretch the entire screen dynamically, you may set the width to a high enough number, which none of your screens exceed (e.g. 10000).

Mako doesn't support this out of the box but is it something that could be added? Right now I'm just hard coding the width of my output into my config but this means I can't easily share my config between machines or use on a machine with different sized outputs.

(I spent a while trying to come up with a patch but I'm out of my depth when it comes to Wayland/wlroots)