Automate package release process

[drborges]

Currently, new package versions are published via npm publish --tolerate-republish.

The plan is to Implement a new Github action that can:

1. Release a new NPM package version every time a Git tag is created;
2. Automatically set the tag @next to be the most recent version released;
3. Create @beta tag when releasing a beta version;
4. Ship Arbor's first beta version, now that its API is fairly stable.

Using semantic-release may be interesting.