Issue:
fix(connector): [Trustpay] add merchant_id in gpay session response for trustpay

## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [x] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
add merchant_id in gpay session response for trustpay

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

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Provide links to the files with corresponding changes.

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1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
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## Motivation and Context
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Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

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## How did you test it?
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Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
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test cases - make a gpay payment for trustpay (in gpay session response, merchant_id should be present). testing of this pr can only be done in prod since this issue was only in prod.
Couldn't test in local.

## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt --all`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible
- [ ] I added a [CHANGELOG](/CHANGELOG.md) entry if applicable


Resolution:
<think>
PR Context:
- Title: fix(connector): [Trustpay] add merchant_id in gpay session response for trustpay
- Merged: 2024-02-02T09:40:03Z
- Files changed: 1 files
- Commits: 1 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [x] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
add merchant_id in gpay session response for trustpay

PR merged in main - #3471

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configurati
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** fix(connector): [Trustpay] add merchant_id in gpay session response for trustpay (#3532)
Files to modify:


**crates/router/src/connector/trustpay/transformers.rs**
  Modify existing code