Allow Auto Devops to access private npm module

Description

If you have a project that depends on a private npm module hosted on https://npmjs.com, Auto Devops will fail to build since it cannot find the private module. As far as I can tell, this makes it impossible to use Auto Devops without copying the Auto-DevOps.gitlab-ci.yml file and editing it to authenticate with with npmjs.

Proposal

Add a predefined environment variable called NPM_AUTH_TOKEN that can store your npm auth token and allow Auto Devops to access your private npm modules.