This is supported https://docs.paloaltonetworks.com/vm-series/10-1/vm-series-deployment/set-up-the-vm-series-firewall-... . You seem to just need to use terraform to specify the bootstrap file and AWS cloudwatch after that will autoscale this https://github.com/PaloAltoNetworks/terraform-aws-panos-bootstrap .
Also you may consider to just use the AWS native palo alto firewall as a service that will autoscale automatically as it is AWS service:
Also look at other posts in the community for possible issues like the one below:
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