Previous version add bugs that were not properly using the _api_key.
It also enforced to provide PANOS_USER and PANOS_PASSWORD which can be very constraining.
PANOS_KEY now has precedence. If not provided, the script falls back to PANOS_USER and PANOS_PASSWORD.
It was discovered in testing that PAN-OS < 9.0 has slightly different
requirements for the multipart/form-data format and requires the `type`
parameter to be passed in the URL. These corrections should work for all
PAN-OS versions.