feat(nixos): add support for gitea/forgejo

[Lichthagel]

Requires fetching release artifacts or building the theme from source (similar to #149)

[isabelroses]

This should now be possible!

[getchoo]

Can't say I'm a fan of introducing a general consts just for this

Maybe access them through types.flavors.functor.payload.values instead?
Now that I type it out it does sound a bit silly, though...

[isabelroses]

I wasn't a fan either hence I wanted to prompt you for a review. Strictly speaking we could drop it again and use IFD. But I'd rather avoid introducing more IFD.

[getchoo]

I think types.flavors.functor.payload.values would be fine for now then, even though it's super ugly

If more ports end up using it later, I'd be fine with a consts

[getchoo]

Sorry for the wait again, I've been setting up my own Forgejo instance for a little bit and figured it would be the perfect place to test this out. I'll hopefully get to it soon :p

[isabelroses]

Sorry for the wait again, I've been setting up my own Forgejo instance for a little bit and figured it would be the perfect place to test this out. I'll hopefully get to it soon :p

On this note. Just deployed my git instance with the theme and it works perfectly.

[getchoo]

With the following applied it works on my Forgejo instance as well :)

[getchoo]

Thanks for your work @Lichthagel and @isabelroses. Sorry for the long wait, too