Add force_update_candles configuration to OKX data collector

- Introduced `force_update_candles` option in `okx_config.json` to control candle update behavior.
- Updated `OKXCollector` to handle candle storage based on the `force_update_candles` setting, allowing for either updating existing records or preserving them.
- Enhanced logging to reflect the action taken during candle storage, improving traceability.
- Updated database schema to include `updated_at` timestamp for better tracking of data changes.

config/okx_config.json

@@ -52,6 +52,7 @@
   "database": {
     "store_processed_data": true,
     "store_raw_data": true,
+    "force_update_candles": false,
     "batch_size": 100,
     "flush_interval": 5.0
   },