Issue:
fix(router): change the retrieve's payload to query

## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [x] Enhancement
- [ ] Refactoring
- [ ] Dependency updates

## Description
Change the deserialisation method from Json to Query in the payments retrieve function
<!-- Describe your changes in detail -->


### Additional Changes

- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!-- Provide links to the files with corresponding changes -->


## Motivation and Context
Based on the requirements for the payments retrieve API to accept parameters instead of fields in the body
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## How did you test it?
Tested the endpoint by sending proper query parameters & by sending no query params
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## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed 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(core): fix merchant connector account create for v2 
- Merged: 2024-08-28T07:56:03Z
- Files changed: 1 files
- Commits: 2 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
 fix merchant connector account create for v2 , by handling the case where defaull fallback is null ,while updating the it


### 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(core): fix merchant connector account create for v2  (#5716)
Files to modify:


**crates/router/src/core/admin.rs**
  Modify existing code