Add a scale option to onagre theme

[Quackdoc]

Is your feature request related to a problem? Please describe. I currently run sway with a 1.2 scale factor on a 4k display, However onagre looks really small like this.

Describe the solution you'd like it would be nice to have a simple scale option in the onagre section of the theme options to uniformly scale up the theme

Describe alternatives you've considered Perhaps a launch option that will allow scaling it up

Additional context

[oknozor]

This is not stabilized but you can now launch onagre like so onagre --scale 2