fix(react-email): Different react-dom version being used to render email templates

[gabrielmfern]

This fixes the issues that were causing #649. What was causing that issue
was that @react-email/render would import react-dom as the Next
bundled version, which would not be the same React instance used
inside the email templates, this caused that globals such as their
dispatcher would not have the expected values.

I noticed this was the cause of that issue after looking at our
updated trace on the error, and it pointed down into the
bundled version of react-dom inside next. The same issue was
also happening for versions prior to 2.0, so this was not a regression either.

To fix this, I added a simple esbuild plugin to when the email template
is loaded, so that it adds a export { renderAsync } from '@react-email/render'
at the end of it. This way, it would also give us access to the renderAsync
and react-dom used in the user's project, so that this mismatch is not there
anymore.

Since I was experimenting a bit as well, I added in a test to make
sure the getEmailComponent function works properly at least with a local
very simple file.

How can I test this?

1. Run pnpm install and turbo build inside packages/react-email
2. Add the following email template at apps/demo/emails/test.tsx

import React from "react";

export default function Test() {
  const containerRef = React.useRef<HTMLDivElement>(null);

  return <div ref={containerRef}>Hello world!</div>;
}

3. Run npx tsx ../../packages/react-email/src/cli/index.ts dev inside apps/demo
4. Open http://localhost:3000/preview/test and verify the error from preview server (email dev) does not work with any React hook #649 does not happen

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Name	Status	Preview	Comments	Updated (UTC)
react-email	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 10, 2024 2:48pm
react-email-demo	❌ Failed (Inspect)			May 10, 2024 2:48pm