Switch database from in-memory to Redis

[sunilagwl5]

Summary

This pull request replaces the existing in-memory data storage mechanism with Redis as the primary database. This change is necessary to persist data across application restarts and improve scalability.

Configuration for Redis connection is expected to be provided via environment variables (REDIS_URL, REDISHOST, REDISPASSWORD, REDISPORT, REDISUSER).

Changes

• Added redis dependency to requirements.txt to support Redis operations.
• Updated main.py to initialize and use a Redis client instead of in-memory lists/variables.
  • Imported redis and json.
  • Introduced get_redis_client() function to establish the connection using environment variables (specifically checking for REDIS_URL).
  • Removed in-memory storage variables (items: List[Item] = [], current_id = 0).

Notes for Reviewers

The implementation for CRUD operations (GET, POST, PUT, DELETE) using Redis is not yet complete in the provided diffs, as the focus here is solely on setting up the Redis connection infrastructure. Reviewers should confirm the environment variable handling for Redis connection is robust.