Allow custom user config file path

[brwai]

Is your feature request related to a problem? Please describe.
Currently ado-npm-auth always looks for user config file under the home directory. This wouldn't work for cases where the project is not located under the user's home directory. It would be better to provide a way to customize where ado-npm-auth locates the user config file.

Describe the solution you'd like
Allow user config file customization through:

1. --userConfigFile option
2. Setting environment variable such as ADO_NPM_AUTH_USER_CONFIG

Please see this PR for suggested changes.