ci: publish preview version of Elysia for testing on pull request

[rayriffy]

Using the same strategy as Vite, this PR will publish a preview version of package that can be used to test the package without needing to publish manually by using pkg.pr.new

Noted that before pkg-pr-new bot can publish, and comment version to GitHub app needed to be installed first. (As described in Setup step)

As a result, when testing with project locally from someone else PR's we can do something like this in package.json

"dependencies": {
  "elysia": "npm:https://pkg.pr.new/elysiajs/elysia@1181"
}