SIENTIAPDE-1712

Enhance README and Implement Drift Detection and Metrics Workflows

- Added new sections in README for Drift Workflow and Simple Metrics Workflow, detailing their execution flows and functionalities.
- Introduced `drift.py` for data drift detection, comparing current data against reference datasets.
- Added `simple_metrics.py` for calculating regression metrics (RMSE, MSE, MAE, R²).
- Updated `values.yaml` to include configuration for MinIO retention hours and offload threshold.
- Refactored `minio_dataframe_payload.py` to use the new offload threshold environment variable.
- Adjusted tests to reflect changes in environment variable handling for MinIO offload threshold.

tests/conftest.py

@@ -2,9 +2,9 @@ import os
 import sys
 from unittest.mock import MagicMock
 
-# The production code converts SIENTIA_MINIO_OFFLOAD_THRESHOLD_BYTES to int at import-time.
+# The production code converts SIENTIA_MINIO_OFFLOAD_THRESHOLD_MEGABYTES to int at import-time.
 # Tests must set it to a valid integer string to avoid import errors.
-os.environ.setdefault('SIENTIA_MINIO_OFFLOAD_THRESHOLD_BYTES', '1')
+os.environ.setdefault('SIENTIA_MINIO_OFFLOAD_THRESHOLD_MEGABYTES', '1')
 
 
 class DummyMinioDataFramePayload: