Release beta 2 and configure npm auto deploy

[difernandez]

Motivation / Background

This Pull Request has been created because:

• We have some unreleased changes
• We have automated the publishing in rubygems but not npm

Detail

This Pull Request:

• Configures CI to publish to NPM whenever a new tag is pushed. Done following this guide
• Bumps gem and npm package version. From this version on, we are going to keep the same version for both. Thanks to @filipkis for their suggestion
• Updates Changelog. Added a beta.1 entry to indicate it was skipped to have both libraries in the same version
• Updates README's Publishing section

Additional information

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a concise description of what changed and why.
• Tests are added or updated if you fix a bug or add a feature.
• Documentation has been added or updated if you add a feature or modify an existing one.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature (under the "Unreleased" heading if this is not a version change).
• My changes don't introduce any linter rule violations.