Publish compiled ASM/WASM packages on NPM

This is a different issue from #8, though has some similarities.

@kelson has suggested that we should publish the compiled javascript-libzim binaries so they can be added to Kiwix JS and Kiwix PWA during CI and also during developer setup through npm install. This would make a lot of sense and would prevent keeping back copies of the binaries in Git history in those repositories.

The steps needed to achieve this here are:

1. Set up the npm package repository (I don't know the right terminology)
2. Probably (I am guessing) add a signing stage to the script that builds the binaries -- I assume NPM would require some verification/security system
3. Modify the workflow so that it will publish the npm package(s) (which should only be done on publishing a release, and also with a workflow dispatch option).

Start with .github/workflows/build_libzim_wasm.yml and review how the compiled JavaScript-libzim binaries are built. Define the npm package setup and any signing or verification requirements, then update the workflow so publication occurs on releases and via workflow dispatch. Done means the compiled ASM/WASM packages can be installed by Kiwix JS and Kiwix PWA through npm.