ci(publish): add publish workflow

[msimerson]

Publish package to NPM and GitHub package registry when:

• a release is manually specified via GitHub interface.
• a PR is merged to master that changes package.json

REQUIRED

• for NPM publishing to work, you must generate a NPM login key with publish privileges. Then store the key in this repositories secrets as NPM_AUTH_TOKEN.
• GPR requires the package scope. An included helper script does the needful.