Dark mode support in splash-screen generator

@fpena is already working on this.

Since Apr 30, 2025.

I'd like to be able to generate the assets for a dark mode splash screen along side the "normal" light mode assets.

Currently, I can call `npx ignite-cli generate splash-screen` and the generator will read logo.png from ignite/templates/splash-screen and output the necessary assets to assets/images. That will work whether logo.png is the image I want to use for light mode or dark mode. The trouble is that if I do one it will overwrite the other and vice versa. I'd like to be able to generate both sets of assets at the same time so I can reference them from my expo app.json

I suggest adding a `--dark` parameter that would tell the generate to read logo-dark.png, output assets that start with "splash-logo-dark" instead of "splash-logo," and update app.json accordingly. But there might be other possible solutions.

I'm happy to take a shot at adding this myself and sending a PR. But I thought it would be wise to make sure something like this wasn't already in the works. And that the solution I suggested above is a valid design.

Thanks!