Auto-publish to NPM registry

[xzwiex]

Automatically publish new version of the library to NPM

Setup

• Create NPM token (https://docs.npmjs.com/creating-and-viewing-access-tokens)
• Add token to project's Secrets (https://docs.github.com/en/actions/security-guides/encrypted-secrets) under name NPM_TOKEN

Action running on every push (or merged PR) to main branch. Publish will be done only if package version has been bumped, so be sure the version in package.json is changed.