Support both terraform and opentofu

[rahearn]

Story

As a devops engineer,
I would like to use terraform-cloudgov with opentofu,
So that I can have more flexibility in my infrastructure stack

Solution

Tasks

Preview Give feedback

1. Investigate what it would take to be compatible with both terraform and opentofu
2. Add ci tests for opentofu (dflook's actions should have opentofu equivalents)

Acceptance Criteria

• Systems can utilize modules with either opentofu or terraform with no other customizations