atlantis: vendor terraform

[iMichka]

This is the last formula in homebrew-core that needs terraform. Vendor it until upstream allows to use openTofu

• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

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[iMichka]

This is the last piece to be able to proceed with #139538

[chenrui333]

• also relates to Support OpenTofu (epic) runatlantis/atlantis#3741

[github-actions]

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