Add monochromatic GLSL to default shaders

[ed-henrique]

I'm using this custom shader, and I thought it could be of use to someone else. So, here it is.

[loqusion]

I want to keep the number of shaders included by default fairly minimal, with exceptions made for those with widespread appeal.

Meanwhile, I believe awesome-hyprland is keeping track of shaders in this issue with plans to keep shaders stored somewhere.

[ed-henrique]

Oh, I didn't know about it, thanks =D