fix(remix): Sourcemaps upload script is missing in the tarball

[Lms24]

To upload source maps to Sentry, the Remix SDK includes a script that wraps around Sentry CLI to make uploading sourcemaps easier for our users. However, due to the way how we package our NPM tarballs, this script didn't make it into the Remix SDK tarball.

This PR adds the script to the tarball, which required the following changes:

• Added a package-specific prepack.ts script which is invoked by the main prepack.ts script. This is similar to how we do it with the Gatsby SDK where - just as with Remix - we need to copy over additional files to the build directory that are not part of our other packages. The newly added files are:
  • scripts/sentry-upload-sourcemaps.js
  • scripts/createRelease.js
• Added a package-specific .npmignore which extends the root level .npmignore file to not ignore the scripts directory in the build directory.

Fixes #5355

[lforst]

Works!