Implement Per-User API Key Management System

[shubhh139]

Create a secure API key management system where users can create and delete API keys for accessing AI4Bharat services.

Acceptance Criteria

• API key generation for security
• API key hashing and secure storage
• API key creation endpoint (POST /api/v1/api-keys)
• API key deletion endpoint (DELETE /api/v1/api-keys/{key_id})
• API key validation middleware
• Database schema for users and api_keys tables
• Alembic migrations for database setup
• Comprehensive test coverage

Estimation: 6 hours