feat: add configuration parsing and job definitions

Add a YAML config schema for migration jobs (source/target schema, table, primary key, options) and parse it at startup.

config.yaml

@@ -0,0 +1,46 @@
+max_parallel_workers: 2
+
+defaults:
+  max_extractors: 4
+  max_loaders: 8
+  queue_size: 8
+  chunk_size: 50000
+  chunks_per_batch: 10
+  truncate_target: true
+  truncate_method: TRUNCATE # TRUNCATE | DELETE
+  retry:
+    attempts: 3
+
+jobs:
+  - name: demo_users
+    enabled: true
+    source:
+      schema: demo
+      table: users
+      primary_key: id
+    target:
+      schema: demo
+      table: users
+    max_extractors: 2 # overrides default config
+    max_loaders: 4 # overrides default config
+    queue_size: 4 # overrides default config
+    chunk_size: 25000 # overrides default config
+    chunks_per_batch: 8 # overrides default config
+    truncate_target: false # overrides default config
+    truncate_method: DELETE # overrides default config
+    retry:
+      attempts: 5 # overrides default config
+    pre_sql:
+      - "SELECT 1"
+    post_sql:
+      - "SELECT 2"
+
+  - name: analytics_events
+    enabled: true
+    source:
+      schema: analytics
+      table: events
+      primary_key: ID_events
+    target:
+      schema: analytics
+      table: events