Ability to create or declare multiple apps

[puchesjr]

Current State of the Art
I am currently utilizing Sveltekit for an internal project leveraging a separate fastify backend for our core api.

Feature Request
As a user, I would like the ability to create either two projects or declare multiple build directories based on paths within svelte.config.js

Benefit
Sveltekit having the ability to create endpoints lends itself well to creating not only the front-end but also the back-end. Unlike the Nextjs model, whereby the API routes are found under domain.com/{api}, I find it may be more beneficial to declare and deploy the API to a separate build directory altogether for deploying to a subdomain e.g., api.domain.com

Proposed model
The default methodology for deploying should be as it is today. Similarly, to how Sveltekit offers the ability to use different adapters, I propose a configuration that can be found in the svelte.config.js file similar. This configuration should ideally include your output directories, app_name, and specific include/excludes for source.

Related Issue
#2930