Allow to override a path to config file

[harnyk]

Problem

Currently, the path to the config file is hardcoded to ./config.yaml and is searched in the current directory.

This behavior is convenient when there are multiple companies and each company has its own config file in a separate directory.

But for a client with a single company, it is inconvenient to have to call the program from the specific directory every time.

Solution

Add a new environment variable ONELOGIN_AUTH_CLI_CONFIG_FILE that, when set, will override the default path to the config file.

A user can set this variable in the shell profile and then call the program from any directory.