Replace getpass with ui.input(hidden=True)

[jbgosselin]

Description

I'm currently trying to automate gimme-aws-creds in a python script.
I admire the idea of the gimme_aws_creds.ui.UserInterface class that helps a lot in automating user input.
I found that some places in the code was directly calling getpass.getpass() and not using the provided UserInterface. Replacing those calls with the proper UserInterface.input(hidden=True).

Related Issue

Fixes #428

Motivation and Context

Allowing developers subclassing gimme_aws_creds.ui.UserInterface for automation to provide inputs for password themselves.

How Has This Been Tested?

• Ran pytest -vv tests with no errors
• Tested it with a script mocking the user input via a subclass of UserInterface.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.