Change (add?) tfid data source into a provider function

[migara]

Starting from Terraform 1.8, provider developers can now add provider functions to perform general util tasks that are not covered by Terraform core util functions.

We can add the generation of a tfid as a provider function

[shinmog]

It seems like custom functions take a specific set of inputs, and then give you an output. Since there are many moving parts to creating a tfid, I'm feeling like the user experience of creating the tfid is better as a data source... especially since creating a tfid now has a rules section which is a list of structs..

These custom Functions also don't get access to the PAN-OS API, so I'm not certain how many useful things we could do with this limitation.