[FEATURE] Support Platform Account to Make Payments for Connected Accounts in VSAAS

### Feature Description

- Enable support for payments processed by a platform merchant on behalf of a connected account.
- Update the MerchantContext enum to accommodate this new flow.
- Adjust how merchant and key store information are accessed and attributed.
- Ensure payments initiated by a platform merchant, but using a connected account’s credentials, are correctly processed.

### Possible Implementation

- Changing Merchant Context to have context for Platform and Connected Accounts as well
- Using Details of merchant context to know about merchant initiating payments and merchant whose connected credentials are getting used.

### 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
<think>
PR Context:
- Title: feat(vsaas): support payments via platform for connected accounts
- Merged: None
- Files changed: 30 files
- Commits: 16 commits

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

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

## Description
This PR introduces a new feature enabling platform merchants to process payments for their connected accounts. This involves adding new context and logic to handle payments initiated by a platform merchant on behalf of a different merchant account (the connected account), supporting a
</think>

To implement this, you'll need to modify:


(No detailed commit information available)
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