AWS_DEFAULT_PROFILE is respected; Path fixes

[kmcquade]

What does this PR do?

• AWS_DEFAULT_PROFILE is now respected by the download and scan-multi-account command. The downloaded filename also respects this instead of using "default" a bunch. Fixes download command should respect AWS_DEFAULT_PROFILE environment variable #237
• Made some formatting updates to the use of Path which should help some of the windows issues. Fixes TypeError: 'PosixPath' object is not iterable 2 #236

Completion checklist

• Additions and changes have unit tests
• The pull request has been appropriately labeled using the provided PR labels
• GitHub actions automation is passing (make test, make lint, make security-test, make test-js)
• If the UI contents or JavaScript files have been modified, generate a new example report:

# Generate the updated Javascript bundle
make build-js

# Generate the example report
make generate-report