Issue:
[REFACTOR]: [Airwallex] Remove Default Case Handling

### :memo: Feature Description

- We utilize match statements to make pivotal decisions, such as generating requests based on the payment method type and managing responses received from the connector. 
- These conditions generally go hand in hand with enum variants. 
- Default case is used because a match statement needs to be exhaustive i.e. every variant needs to be covered. 
- So, if all the explicit cases are handled then default is used to handle the rest.
- Each connector have these match statements but many of them don’t provide reference to each variant in their default case, rather a `_` is put to handle all the other cases. 
- This approach carries a risk because developers may inadvertently overlook the need for explicit handling of the new cases.

### :hammer: Possible Implementation

- Instead of relying on a default match case `_`, developers should handle each and every variant explicitly. 
- By doing so, if there are any changes in the future, they can readily assess the impact of their modifications simply by compiling the code.
- You can check this PR for further reference https://github.com/juspay/hyperswitch/pull/1955

:bookmark: Note: All the changes needed should be contained within `hyperswitch/crates/router/src/connector/`


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

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

### :package: Have you read the Contributing Guidelines?

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

### :sparkles: Are you willing to submit a PR?


Resolution:
<think>
PR Context:
- Title: refactor(connector): [Airwallex] Remove default case handling
- Merged: 2023-10-27T12:12:59Z
- Files changed: 1 files
- Commits: 1 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [x] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
#2262 

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!--
Provide links to the files with correspond
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** refactor(connector): [Airwallex] Remove default case handling (#2703)
Files to modify:


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

**Commit 2:** refactor(connector): [Airwallex] Remove default case handling (#2703)
Files to modify:


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