[ ENH ] Provide headers when returning 401 failures via the Uber class

[jshcodes]

Describe the enhancement
When you fail authentication using the Uber class and are returned a 401, the headers branch of the Result object is empty. Populate this branch with the headers from the authentication failure.

To Reproduce
Create an instance of the Uber class using invalid authentication, then immediately make a call to the command method. When you are returned the 401, the headers branch is an empty dictionary.

{'status_code': 401, 'headers': {}, 'body': {'errors': [{'message': 'Failed to issue token.'}], 'resources': []}}

Expected behavior
The headers branch should be populated with the headers dictionary produced when the authentication failure occurs.

Environment (please complete the following information):

• OS: All supported
• Python: All supported
• FalconPy: <= 1.0.5

Additional context
Authentication occurs in this scenario as a background request, resulting in these headers being discarded.

Thanks to @tsullivan06 for suggesting this enhancement.