transparent_background and other options for catppuccin/nvim

[reinux]

There's a slew of options for catppuccin/nvim that might be worth being able to set.

On the other hand, the other apps catppuccin configures don't seem to have so many options made available, so I'm not sure if we want to expose all of them through catpppuccin/nix. (Cava does have a transparency option.)

I did make a fork with the transparent_background option, but I don't want to make a PR just yet, because this is my first time writing options for any nix packages, and I'm not confident regarding style and conventions etc. (e.g. do we keep the snake case?)

Any guidance would be appreciated!

[getchoo]

a freeform module would probably be ideal here as we wouldn't need to constantly update our options to reflect the upstream port

PRs are welcome here