Please add the option for specifiying Node Audit credentials

**Is your feature request related to a problem? Please describe.**
Currently, there is no option to specify credentials for the Node Audit analyzer. In my case, I have to use a private company-managed Artifactory instance (that supports Node Audit). This works from the command line when `npm` is properly configured. I can specify the Node Audit URL for dependency-check via `analyzer.node.audit.url` property but the server responds with a 401 Unauthorized error due to missing credentials.

**Describe the solution you'd like**
I would like to have the option to specify the credentials when using a custom Node Audit endpoint. Similar to the `analyzer.ossindex.user` and `analyzer.ossindex.password` properties (or their direct configuration counterparts).

**Describe alternatives you've considered**
The short-term alternative for me would be to proxy the request in some way. I think using a custom Node Audit URL will require proper authentication in most scenarios. So therefore, this should be a feature of DependencyCheck directly.

**Additional context**
None.