feat(react-email): No forced file extensions on slugs

[gabrielmfern]

What was the issue?

Users were being forced into always having a .tsx at the end of the path
for the preview app, this fixes that, meaning that if the user navigates around
between emails there won't be any .tsx, but if the user opens the URL
with an existing email and the right file extension, it will render correctly as well.

The latter remark from above is important because it means that we don't really
have to update the docs again to match these paths but the paths are still
going to look better for user experience.

How can I test to make sure it's fixed?

1. Run npx tsx ../../packages/react-email/src/cli/index.ts dev inside of ./apps/demo
2. Open http://localhost:3000/preview/airbnb-review.tsx and verify that it works
3. Open http://localhost:3000/preview/aribnb-review and verify it also works
4. Navigate between emails and verify that they don't have any .tsx file extension on the URL

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
react-email	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 15, 2024 5:19pm

1 Ignored Deployment

Name	Status	Preview	Comments	Updated (UTC)
react-email-demo	⬜️ Ignored (Inspect)	Visit Preview		Feb 15, 2024 5:19pm

[bukinoshita]

Should we actually support extensions in the URL? How hard would be to not support it?

[bukinoshita]

When having .tsx in the url for example, the sidebar item is not active

[gabrielmfern]

Should we actually support extensions in the URL? How hard would be to not support it?

@bukinoshita I don't think it would be hard but we'd need to change the links on the docs again through another PR maybe. Wdyt about that?

[gabrielmfern]

Thank you so much @vcapretz!