Set up CodeSandbox CI (#679)

Hi @nene 👋  

Wanted to check whether you'd be open to installing the [CodeSandbox
CI](https://codesandbox.io/docs/learn/ci) GitHub app to create an
installable package on each PR.

Example (`@upleveled/preflight`):

- Comment in PR
upleveled/preflight#481 (comment)
- Installable package
https://ci.codesandbox.io/status/upleveled/preflight/pr/481/builds/444571
![Screenshot 2023-12-01 at 14 57
50](https://github.com/sql-formatter-org/sql-formatter/assets/1935696/7ceb467f-2f57-4973-9898-d6c3802e702a)

If you're open to this, then you'd need to merge this PR and also
install [the CodeSandbox CI GitHub
App](https://github.com/apps/codesandbox-ci)

.codesandbox/ci.json

@@ -0,0 +1,3 @@
+{
+  "node": "18"
+}