What this PR does / why we need it:

• Implement HTTP connection pooling for the remote online store client to improve latency by reusing TCP/TLS connections across requests
• Add configurable connection pool settings via feature_store.yaml: connection_pool_size, connection_idle_timeout, and connection_retries
• Add automatic idle timeout to close stale sessions and release resources
• Add thread-safe session management via HttpSessionManager class

Misc

New Features

• Connection Pooling: HTTP sessions are now cached and reused, eliminating TCP/TLS handshake overhead (~40-130ms) on subsequent requests
• Configurable Settings: Users can customize pool size, idle timeout, and retry behavior in feature_store.yaml
• Automatic Idle Timeout: Sessions are automatically closed after configurable idle period (default: 5 minutes)
• Retry with Backoff: Built-in exponential backoff retry logic for transient failures

Configuration Options

online_store:
  type: remote
  path: http://feast-feature-server:80
  connection_pool_size: 50        # Max connections in pool (default: 50)
  connection_idle_timeout: 300    # Idle timeout in seconds (default: 300, 0 to disable)
  connection_retries: 3           # Retry count with backoff (default: 3)