Add delete function for AccessPackageResourceRoleScope

[alexwilcox9]

Hey @manicminer

Hoping this can help towards resolving hashicorp/terraform-provider-azuread#1091
Once the delete function is merged it can be referenced in this function:
https://github.com/hashicorp/terraform-provider-azuread/blob/main/internal/services/identitygovernance/access_package_resource_package_association_resource.go#L146-L150

Errors should still be expected if a user has been assigned a given resource but this will at least allow things to delete when no assignments are in place

Let me know if any tweaks are needed!

[alexwilcox9]

The second commit addresses a bug I've noticed where if a azuread_access_package_resource_package_association is deleted by a user in the console terraform errors rather than seeing the resource has gone and removing it from state

This happens because the AccessPackageResourceRoleScopeClient.Get function returns the status of the HTTP request to the accessPackages endpoint which does succeed but then as it parses the output and fails to find a matching entry it does not update that status to 404
The above results in this if statement never firing
https://github.com/hashicorp/terraform-provider-azuread/blob/main/internal/services/identitygovernance/access_package_resource_package_association_resource.go#L124-L127

If it is more appropriate to always hand back the status code from the endpoint and instead this should be handled in the Terraform code let me know and I'll role this commit back

[manicminer]

Thanks @alexwilcox9, this LGTM.

Great spot on the missing resource bug. I think it's fine to fake a 404 error for now, this will be the least painful fix. We'll likely do it slightly differently in future but this works for now 👍