Support Preview Deployments with Hosting rewrites to Cloud Functions

### The use case you're trying to solve

Deploy SSR web apps with Preview Deployments.

Current solutions require an entire separate project for `dev` and `prod` with `dev` being shared amongst developers, or relying solely on local emulation which is not quite as robust as a full env deployment.

### Change to the action that would solve that use case

There would need to be a new Cloud Function for the Preview Deployment (PR prefix etc) with the rewrite config updated on deployment for the Hosting Preview Channel.

### Other considerations

I believe I requested this feature about a year ago, perhaps in the Google Group, but have seen no update.

**Additional info**

I have written about [SSR web apps on Firebase](https://github.com/jthegedus/firebase-gcp-examples) with various frameworks and authored the [Firebase adapter](https://github.com/jthegedus/svelte-adapter-firebase) for [SvelteKit](https://kit.svelte.dev/).