Upgrade `deploy_npm` for newer NPM versions

[flyingsilverfin]

Because of the changes noted in #372, we no longer have a consistent behaviour: NPM deployment works either with username/password OR tokens depending on the environment variables provided.

To attempt to rectify this, we should consistently use token-based authentication if we can. Part of this process should include upgrading deploy_npm to be compatible with newer versions of NPM - it currently requires NPM 8.x to deploy Vaticle's artifacts.

Note: a related but also important step would be to upgrade the testing and snapshot repositories used (eg. Sonatype) to the latest versions.

[alexjpwalker]

NB we are planning to migrate to a hosted provider at some point to replace our current self-hosted Nexus repository, and should prefer doing this rather than attempting to upgrade our self-hosted installation.