feat: add @zeabur/svelte-adapter support in adapter-auto

[yuaanlin]

Introduce support for @zeabur/svelte-adapter in adapter-auto.

This PR simplifies the deployment process for developers aiming to host their Svelte applications on Zeabur.

It eliminates the need for manual installation and configuration updates, as outlined in the Zeabur documentation (https://zeabur.com/docs/guides/nodejs/svelte-kit#step-2-set-up-zeabursvelte-adapter).

Example Svelte Kit website deployed on Zeabur with @zeabur/svelte-adapter: https://svelte-kit.zeabur.app/

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🦋 Changeset detected

Latest commit: 8014fb4

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/adapter-auto	Minor

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[benmccann]

I've never particularly liked that this file is a kitchen sink for various adapters. I don't know if we want a giant list of relatively new and unknown hosting providers here. At the same time, it would be nice if adapter-auto didn't work only for the major players.

Perhaps we need a new way to handle this like process.env.SVELTEKIT_DEFAULT_ADAPTER and process.env.SVELTEKIT_DEFAULT_ADAPTER_VERSION could specify to download and use @zeabur/svelte-adapter version 1 and then we don't need to update this file whenever a new hosting provider would like to list their platform as they could provide those environment variables instead.