Added boilerplate to create/bundle an npm package on Github, so that
the build artifact(s) can be included in the static files of the
django app for ease of use, and other projects can separately install
the package for the JS with npm to bundle the JS with their own
solution.

The added type safety helps catch bugs, and the setup is simple enough
for people not too familiar with TS to be able to contribute.

Small refactors have been done to avoid globals and localize state a
bit more, which shouldn't affect anyone.

The cookiebar module TS source is taken as input, and the
resulting bundle written to the cookie consent staticfiles
directory.

The onShow handler should be invoked after the node was inserted.

Thanks to @grrodre for contributing the patch!

The npm 'package' and the django staticfiles assets are exclusively
to be built in the CI pipeline, and not kept in version control.

This keeps a single source of truth and prevents us from forgetting to
update the artifacts, at the cost of a little extra step for local
development.

Ensure that the frontend package version is also bumped.

A package with type: module requires extensions in the imports to
fully resolve them (tested with Webpack 5). We can simply use the .js
extension even in .ts files, tsc understands it (even though this looks
really weird).

The code is different from 0.5.0 beta 0, and the next release will
be 0.6.0.