fix: ngfw subnet_mapping change from TypeList to TypeSet

[ahuseby]

Description

fixes https://github.com/PaloAltoNetworks/terraform-provider-cloudngfwaws/issues/30

Motivation and Context

Bugfix for input subnet_mappings in the ngfw resource. See issue: https://github.com/PaloAltoNetworks/terraform-provider-cloudngfwaws/issues/30.

How Has This Been Tested?

Tested by planning and applying locally on my macbook. If I adjust the number of subnet mappings, e.g I have 3 subnet mappings to eu-north-1a, eu-north-1b, eu-north-1c and remove the one for eu-north-1c, it looks like all 3 are removed then re-added. However this seems to only be only how Terraform observes and updates the state; in NGFW only the relevant endpoint is removed.

Currently there are no acceptance tests for this resource. Writing tests for ngfw resource requires an AWS account for provisioning VPC resources.

Screenshots (if appropriate)

n/a

Types of changes

Bug fix

Checklist

• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document. (where?)
• [ ] I have added tests to cover my changes if appropriate.
• [ ] All new and existing tests passed.

[ahuseby]

https://github.com/PaloAltoNetworks/terraform-provider-cloudngfwaws/issues/30 seems to have been caused by a tainted ngfw instance.