refactor get-terraform-dir to remove duplication between jobs

[james3ware]

get-terraform-dir should use a single file type list that is used to populate both jobs so that changes are only required in one place. This isn't urgent, because the likely hood of the terraform file types changing is low.

[chris3ware]

We might not be using this action now because terraform-docs uses the native find feature and we are currently testing trunk-io code quality which would replace the lint workflow.