migrate legacy advantage shopping and advantage app campaigns to meta's unified advantage+ structure via the marketing api

Steps

1. Check the campaign's smart_promotion_type field to identify legacy Advantage Shopping (AUTOMATED_SHOPPING_ADS) or Advantage App (SMART_APP_PROMOTION) campaigns.
2. For new campaigns, configure the three Advantage+ automation levers directly: a campaign-level budget with a supported bid strategy, targeting_automation with advantage_audience enabled, and no placement targeting or exclusions.
3. Migrate eligible existing ASC campaigns via the Copies endpoint with the migrate_to_advantage_plus field, or update in place with the same field to preserve the original campaign ID.
4. Read back advantage_budget_state, advantage_audience_state, and advantage_placement_state to confirm the campaign fully reflects an ADVANTAGE_PLUS_* advantage_state.
5. For accounts relying on existing_customer_budget_percentage, implement the two-ad-set workaround (a custom-audience ad set with relaxation disabled, plus an excluding twin ad set) ahead of the field's removal.