feat(terraform): add support for OpenTofu (.tofu/.tofu.json) file extensions

[srivamsia]

Summary

Adds native support for scanning OpenTofu configuration files using the
.tofu and .tofu.json extensions.

Motivation

OpenTofu is a community-driven fork of Terraform that commonly uses the
.tofu file extension. At present, Checkov does not detect these files,
which prevents users from scanning OpenTofu-based IaC projects.

Changes

• Extend Terraform file discovery to include .tofu and .tofu.json
• Update parser and runner logic to treat .tofu files equivalently to .tf
• Add unit tests to validate parsing and scanning behavior for .tofu files

Testing

• Added new unit tests under tests/terraform
• Verified that Checkov detects and parses resources defined in .tofu files