[FEATURE] Alter refund schema to support VSAAS cases

### Feature Description

Make changes to support the integration of the (VSAAS) into the refund flow. The new columns, `processor_merchant_id` and `created_by`, are essential for storing specific information related to VSAAS transactions within the refund record. 
This will allow for better tracking and management of refunds, which is a key requirement for Vertical SaaS implementations.

### Possible Implementation

Add new columns to refunds schema

### Have you spent some time checking if this feature request has been raised before?

- [x] I checked and didn't find a similar issue

### Have you read the Contributing Guidelines?

- [x] I have read the [Contributing Guidelines](https://github.com/juspay/hyperswitch/blob/main/docs/CONTRIBUTING.md)

### Are you willing to submit a PR?

Yes, I am willing to submit a PR!
<think>
PR Context:
- Title: feat(refunds): add new columns in refund table for vsaas
- Merged: None
- Files changed: 9 files
- Commits: 1 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [x] New feature
- [ ] Enhancement
- [x] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
This PR adds new columns to the `refund` table to support VSAAS functionality.

This PR introduces changes to add new columns (`processor_merchant_id`, `created_by`) to the `refund` table and integrate them into the application logic to support Vertical SaaS (VSAAS).

## Changes

</think>

To implement this, you'll need to modify:


(No detailed commit information available)
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