Implementation of official OpenTofu support

[ilithanos]

Lets have a discussion about how we want to go about implementing official openTofu support to the tofu-controller.

Currently it's supported by replacing the binary used in the runners, but that is more a hacky solution than a real solution.

There are multiple ways to go about this, but since we've mentioned before that main focus will be OpenTofu support with their compatibility with Terraform being secondary but still good to have, we need to consider how to go about implementing it.

Currently we are using hashicorps package for interacting with the terraform binary, openTofu has their own fork of this package, and it could be a solution to migrate to using OpenTofus package instead. That also ensures that we won't end up hitting any license issues from hashicorp.

Another way could be to simple let the user select which binary is used in the deployment configuration. But at some point we might see the two projects go down different roads with specific features being incompatible.

How do you guys think we should go about this?

@chanwit @yitsushi @ArieLevs tagging you guys here to make you aware of this discussion as a place to keep OpenTofu implementation and design discussions in one place.

[ilithanos]

My suggestion would be to consider moving to using https://github.com/opentofu/tofu-exec instead of tf-exec if our main focus is going to move to supporting opentofu with terraform backwards compatability.