refactor: replace per-dialect extractors with generic extractor

Collapse the mssql- and postgres-specific extractors into a single generic implementation driven by the DB dialect interface.

internal/app/etl/transformers/mssql.go

@@ -119,11 +119,13 @@ func computeStorageTransformationPlan(
 						schema, table, sourceColName, v)
 					return v, nil
 				}
-				blobPath := fmt.Sprintf("%s/%s/%s/%s.bin", schema, table, sourceColName, uuid.New().String())
+				start := time.Now()
+				blobPath := fmt.Sprintf("%s/%s/%s", schema, table, uuid.New().String())
 				blobURL, err := azureClient.UploadAndGetURL(ctx, blobPath, b)
 				if err != nil {
 					return nil, fmt.Errorf("uploading %s.%s.%s: %w", schema, table, sourceColName, err)
 				}
+				log.Debugf(`Succesfully uploaded "%s", (%vms)`, blobURL, time.Since(start).Milliseconds())
 				return blobURL, nil
 			},
 		})