Issue:
feat(session_token): serialize with camelCase for gpay token

## Type of Change
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- [x] Refactoring

## Description
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Send the google pay session token ( taken from metadata ), in camelCase since google pay is expecting it in camelCase.

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## Motivation and Context
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Refactoring request from the frontend team


## How did you test it?
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![Screenshot 2023-01-09 at 3 26 36 PM](https://user-images.githubusercontent.com/48803246/211281999-51943c39-5826-4d54-a471-208efdad944e.png)


## Checklist
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- [x] I formatted the code `cargo +nightly fmt`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed submitted code


Resolution:
<think>
PR Context:
- Title: revert: serialize with camelCase for gpay token
- Merged: 2023-01-11T09:55:12Z
- Files changed: 2 files
- Commits: 3 commits

Implementation approach:
Reverts juspay/hyperswitch#324

In order to maintain consistency in the api, it has been decided that this transformation will be done in the frontend. @bernard-eugine 
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** revert: serialize with camelCase for gpay token (#328)
Files to modify:


**crates/api_models/src/payments.rs**
  Modify existing code

**crates/router/src/core/payments/flows/session_flow.rs**
  Modify existing code