This script adds NPM registry authentication through the .npmrc file in the
current directory. If no .npmrc file exists, it is created, otherwise the
authentication is appended to the existing file.
--registry: For which registry to set authentication, e.g. npm.ambassify.eu. If not set, it will use npm's NPM_CONFIG_REGISTRY environment variable or default to registry.npmjs.org if it isn't present.
--env: The environment variable that contains the token for authentication. If the variable isn't set, no authentication will be added. Defaults to NPM_TOKEN.