feat: integrate azure storage handling in migration pipeline

Stream transformer output to an Azure blob container when a job declares ToStorage, with per-job prefix and credential configuration.

config.yaml

@@ -28,8 +28,8 @@ jobs:
     target:
       schema: demo
       table: users
-    pre_sql: 
-      - 'SELECT 1'
+      pre_sql: 
+        - 'SELECT 1'
     range:
       min: 1000000
       max: 2000000
@@ -45,7 +45,21 @@ jobs:
     target:
       schema: analytics
       table: events
-    pre_sql: 
-      - 'SELECT 1'
-    post_sql: 
-      - "SELECT 1"
+      pre_sql: 
+        - 'SELECT 1'
+      post_sql: 
+        - "SELECT 1"
+
+  - name: storage_attachments
+    source:
+      schema: analytics
+      table: attachments
+      primary_key: id
+    target:
+      schema: analytics
+      table: attachments
+    to_storage:
+      columns:
+        - source: DATA
+          target: FILE_URL
+          mode: REFERENCE_ONLY # REFERENCE_ONLY | DUPLICATE_WITH_REF