<!-- Describe your changes in detail -->
This PR adds support for propagating merchant_reference_id for PaymentsAuthorizeData v2.
To implement this **search_filter** feature, you'll need to modify these architectural layers:


**1. Core Business Logic**
   - `crates/router/src/core/payments/transformers.rs`

**Code Patterns Applied:**
- Extend existing types with new fields (1 changes)
{"pr_number": 9013, "pr_title": "refactor(core): propagate merchant_reference_id for PaymentsAuthorizeData", "merged_at": "2025-08-21T16:12:01Z", "intent": {"feature_type": "search_filter", "action": "add_feature", "entities": ["customer", "payment", "merchant"]}, "hierarchy": {"core_business": ["crates/router/src/core/payments/transformers.rs"]}, "change_types": {"fields_added": 1}, "has_identifier_data": false, "commits_matched": 0, "match_method": "none"}