[BUG] - [Adyen] Add Subscription to AdyenRecurringProcessingModel enum

### Bug Description

In CIT MOTO payments, the RecurringProcessingModel was received as Subscription, which caused a deserialization error.

### Expected Behavior

This has been resolved by adding Subscription to the AdyenRecurringModel enum.

### Actual Behavior

This has been resolved by adding Subscription to the AdyenRecurringModel enum.

### Steps To Reproduce

Provide an unambiguous set of steps to reproduce this bug. Include code or configuration to reproduce, if relevant.
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### Context For The Bug

_No response_

### Environment

Are you using hyperswitch hosted version? Yes/No
If yes, please provide the value of the `x-request-id` response header to help us debug your issue.

If not (or if building/running locally), please provide the following details:
1. Operating System or Linux distribution:
2. Rust version (output of `rustc --version`): ``
3. App version (output of `cargo r --features vergen -- --version`): ``

### Have you spent some time checking if this bug 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, I am willing to submit a PR!