Adder for sveltekit adapter

[benmccann]

auto should be the default. also offer other official adders

can also use it to customize ignores. see #335

[manuel3108]

Should this be an adder? Or a question while creating a new project, similar to the types question? How would we call the adder?

[benmccann]

Interesting. I hadn't considered offering it only during the project setup. I guess that's an option. Though switching out adapter-auto with an adder seems nice

We could call it sveltekit-adapter