feat: add support for opentofu

[LucasMrqes]

This makes it possible to use opentofu instead of terraform. It involves some CRD modifications:

• Terragrunt configuration is no longer under terraform config in TerraformRepository & Layer spec
• One can choose between terraform and opentofu as base executor for infra as code in layer and repositories config with spec.terraform.enabled and spec.terragrunt.enabled
• Validation rules prevent users from setting both parameters to true
• Layer config overrides Repo config.

Todo:

• Update CRDs
• Integrate opentofu to runner
• Add tests, specifically for parameter merge edge cases
• Fix test data used in runner & end-to-end tests
• Update documentation
• Better, dynamic logging with less hardcoded references to "terraform"

[corrieriluca]

I think we can abstract the tool used to have only one property. For Terragrunt, we only need the execution path of the tool.

I see 2 solutions:

1. We add another function to the TerraformExec interface to obtain the execution path of the tool
2. We just give a string BaseToolPath to the Terragrunt struct instead of a pointer to an object

[LucasMrqes]

I like the first idea, but this makes the exec patterns a little more complicated tho; check my last commit, wdyt ?

[corrieriluca]

Overall very great Pull Request! 👏
It opens Burrito to the world of OpenTofu 😄