`terraform.yaml` workflow should look and work for all modules

### Problem statement

Currently, the workflow expects users to pass a [`module-directory`](https://github.com/canonical/workflows-team/blob/main/.github/workflows/terraform.yaml#L9) which will contain the terraform module under test. This is great for repositories with a single module, but in repositories with various, this no longer works.

### Enhancement Proposal

To perform a search from the root or an arbitrary directory to find any Terraform modules and run tests on all the found ones (parallelly).

### What needs to get done?

1. Remove the `module-directory` input
2. Create a tiny script that looks for all modules in a repo or directory
3. Ensure the tests run for all the found modules