feat: use preinstalled Terraform if available with specific version

[Hi-Fi]

Related issue

Fixes #178

Description

Action will check availability of Terraform in PATH with version configured to action. If there's suitable version available, it doesn't download Terraform.

Checklist

• [x] I have updated the PR title to match CDKTF's style guide
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works if applicable
• [x] New and existing unit tests pass locally with my changes

[github-actions[bot]]

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