Add Git VCS transformer for GitHub/GitLab repos

[AkashS0510]

Summary

• Adds a new Git VCS transformer (transformer/git-vcs/) that scans GitHub or GitLab organizations for Terraform repositories and generates sg-payload.json for bulk workflow import via sg-cli
• Installable as a CLI tool (sg-git-scan) — no need to run raw Python scripts
• Supports monorepo detection (each Terraform directory becomes a separate workflow), cloud provider inference from HCL provider blocks, Terraform version parsing from required_version, and both GitHub and GitLab APIs

What's included

• sg_git_scan/cli.py — CLI entrypoint with argparse (--provider, --token, --org, etc.)
• sg_git_scan/vcs.py — Lightweight GitHub/GitLab API clients (Git Trees API, Repository Tree API)
• sg_git_scan/scanner.py — IaC detection from file trees + HCL parsing (providers, versions, tfvars)
• sg_git_scan/transform.py — Maps discovered repos/projects to SG workflow payloads
• example_payload.jsonc — Annotated reference for the output schema
• README.md — Full usage docs, CLI options, post-generation editing guide
• Updated top-level README.md to list Git VCS as a supported platform

Usage

cd transformer/git-vcs
pip install .
sg-git-scan --provider github --token ghp_xxx --org my-org
# Edit sg-payload.json as needed, then:
sg-cli workflow create --bulk --org "<ORG>" -- sg-payload.json