feat: introduce Terraform for AWS infrastructure management

[AnzalKhan16]

📌 Overview
Introduced Infrastructure as Code (IaC) using Terraform to manage the AWS infrastructure for CropChain.
This configuration accurately provisions the VPC, Subnets, Internet Gateway, Security Group, IAM Roles for SSM, and the EC2 backend instance. The Terraform configuration is modularized into main.tf, providers.tf, variables.tf, and outputs.tf in the infrastructure/ directory. An example terraform.tfvars.example is provided, avoiding any hardcoded secrets. Additionally, I added Terraform formatting (terraform fmt) and validation (terraform validate) checks to the CI workflow (ci.yml) to ensure continuous IaC health.

🛠️ Type of Change
[ ] ⛓️ Smart Contract (Solidity changes, Gas optimization)
[ ] 💻 Frontend (UI/UX, React components, Tailwind)
[ ] ⚙️ Backend (API routes, MongoDB schemas, Middleware)
[x] 📄 Documentation (README, Roadmap updates)
[x] 🧪 Testing (CI/CD Pipeline, DevOps & Infrastructure as Code)

🔗 Related Issue
Closes #845

🧪 Testing & Verification
Smart Contracts: npx hardhat test passed? (NA)
Frontend: Verified on Mobile/Desktop responsiveness? (NA)
Integration: Verified ethers.js connectivity with local/testnet node? (NA)

📸 Screenshots / Demos
(N/A - Infrastructure updates only)

✅ PR Checklist
[x] My code follows the project's style guidelines.
[x] I have commented my code, particularly in complex areas (e.g., Smart Contract logic).
[x] I have updated the documentation accordingly.
[x] My changes generate no new warnings.

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