Add new cli option for user_api_key

Adding a new command line option —user_api_key to allow passing an api key to the fury cli to prevent being prompted for login credentials.

When using the Fury CLI from either a continuous integration system or with a user account that was created from a GitHub user account, the standard prompt for user credentials does not work correctly.  We would like to be able to push gems to gemfury in both of these situations using the CLI instead of using the website or curl.