Add a multi-key sync support

[Yostra]

Summary

• Adds support for syncing multiple Stripe accounts into a single Postgres schema. Each row includes an _account_id column with the real Stripe account ID, and tables use a composite primary key (id, _account_id) so records from different accounts coexist without collisions.
• Introduces a sync-multi CLI subcommand that accepts a JSON config with multiple pipelines, auto-resolves Stripe account IDs from API keys, runs setup sequentially (to avoid Postgres schema creation races), then syncs all pipelines concurrently.
• Uses the resolved account ID as the syncId for the state store, so page cursors are isolated per account and don't interfere across pipelines.

How to test (optional)

replace STRIPE_API_KEY_1 and STRIPE_API_KEY_2 with actual keys

node apps/engine/dist/cli/index.js sync-multi --config '{
  "pipelines": [
    {
      "source": { "name": "stripe", "api_key": "[STRIPE_API_KEY_1]" },
      "destination": {
        "name": "postgres",
        "connection_string": "postgresql://postgres:postgres@localhost:55432/postgres?sslmode=disable",
        "schema": "stripe"
      },
      "streams": [{ "name": "customers" }]
    },
    {
      "source": { "name": "stripe", "api_key": "[STRIPE_API_KEY_2]" },
      "destination": {
        "name": "postgres",
        "connection_string": "postgresql://postgres:postgres@localhost:55432/postgres?sslmode=disable",
        "schema": "stripe"
      },
      "streams": [{ "name": "customers" }]
    }
  ]
}'