Add support for Terraform Exclusions

[hattan]

The current terraform implementation is lacking support for layer exclusion (excludedFolders), which is supported in Bicep.

This work item is to bring parity between Bicep and Terraform implementations in Symphony to ensure we support folder exclusion.

A.C. - Terraform Projects (on both AzDo and GitHub Actions) should support layer exclusions.

[lukemurraynz]

Just came here to raise an issue about this, scenario, in Azure DevOps with Terraform:

\Terraform IaC Folder\JSON files and other supporting scripts

It keeps trying to run a terraform init and plan across it. I attempted a terraformignore file, but didn't make a difference. In my scenario I will end up with 50-100 supporting files and rather not have these in the base folder, if I can avoid it, It is causing my build to fail, and even if I had a provider.tf into the supporting folder, it skips my actual Terraform IaC folder.