Support aws-vault instead of named AWS profiles

[kouk]

Description

Update the AWS function to optionally retrieve the profile name from the AWS_VAULT environment variable instead of AWS_PROFILE.

Motivation and Context

When using 99designs/aws-vault the variable AWS_VAULT is set to indicate which profile has been configured in the environment and the AWS_PROFILE environment variable is not set. This commits makes AWS_VAULT override the profile name.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

• [x] I have tested using MacOS
• [ ] I have tested using Linux

Checklist:

• [x] I have checked that no other PR duplicates mine
• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have updated the tests accordingly.